// bslstl_multimap.h                                                  -*-C++-*-
#ifndef INCLUDED_BSLSTL_MULTIMAP
#define INCLUDED_BSLSTL_MULTIMAP

#include <bsls_ident.h>
BSLS_IDENT("$Id: $")

//@PURPOSE: Provide an STL-compliant multimap class.
//
//@CLASSES:
//   bsl::multimap: STL-compatible multimap template
//
//@CANONICAL_HEADER: bsl_map.h
//
//@SEE_ALSO: bslstl_map, bslstl_multiset
//
//@DESCRIPTION: This component defines a single class template,
// `bsl::multimap`, implementing the standard container holding an ordered
// sequence of key-value pairs (possibly having duplicate keys), and presenting
// a mapping from the keys (of a template parameter type, `KEY`) to their
// associated values (of another template parameter type, `VALUE`).
//
// An instantiation of `multimap` is an allocator-aware, value-semantic type
// whose salient attributes are its size (number of key-value pairs) and the
// ordered sequence of key-value pairs the multimap contains.  If `multimap` is
// instantiated with either a key type or mapped-value type that is not itself
// value-semantic, then it will not retain all of its value-semantic qualities.
// In particular, if either the key or value type cannot be tested for
// equality, then a `multimap` containing that type cannot be tested for
// equality.  It is even possible to instantiate `multimap` with a key or
// mapped-value type that does not have a copy-constructor, in which case the
// `multimap` will not be copyable.
//
// A multimap meets the requirements of an associative container with
// bidirectional iterators in the C++ standard [23.2.4].  The `multimap`
// implemented here adheres to the C++11 standard when compiled with a C++11
// compiler, and makes the best approximation when compiled with a C++03
// compiler.  In particular, for C++03 we emulate move semantics, but limit
// forwarding (in `emplace`) to `const` lvalues, and make no effort to emulate
// `noexcept` or initializer-lists.
//
///Requirements on `KEY` and `VALUE`
///---------------------------------
// A `multimap` is a fully "Value-Semantic Type" (see {`bsldoc_glossary`}) only
// if the supplied `KEY` and `VALUE` template parameters are themselves fully
// value-semantic.  It is possible to instantiate a `multimap` with `KEY` and
// `VALUE` parameter arguments that do not provide a full set of value-semantic
// operations, but then some methods of the container may not be instantiable.
// The following terminology, adopted from the C++11 standard, is used in the
// function documentation of `multimap` to describe a function's requirements
// for the `KEY` and `VALUE` template parameters.  These terms are also defined
// in section [17.6.3.1] of the C++11 standard.  Note that, in the context of a
// `multimap` instantiation, the requirements apply specifically to the
// multimap's entry type, `value_type`, which is an alias for 'pair<const KEY,
// VALUE>'.
//
// ```
// Legend
// ------
// 'X'    - denotes an allocator-aware container type (e.g., 'multimap')
// 'T'    - 'value_type' associated with 'X'
// 'A'    - type of the allocator used by 'X'
// 'm'    - lvalue of type 'A' (allocator)
// 'p',   - address ('T *') of uninitialized storage for a 'T' within an 'X'
// 'rv'   - rvalue of type (non-'const') 'T'
// 'v'    - rvalue or lvalue of type (possibly 'const') 'T'
// 'args' - 0 or more arguments
// ```
//
// The following terms are used to more precisely specify the requirements on
// template parameter types in function-level documentation.
//
//: *default-insertable*: `T` has a default constructor.  More precisely, `T`
//:     is `default-insertable` into `X` means that the following expression is
//:     well-formed:
//:      `allocator_traits<A>::construct(m, p)`
//:
//: *move-insertable*: `T` provides a constructor that takes an rvalue of type
//:     (non-`const`) `T`.  More precisely, `T` is `move-insertable` into `X`
//:     means that the following expression is well-formed:
//:      `allocator_traits<A>::construct(m, p, rv)`
//:
//: *copy-insertable*: `T` provides a constructor that takes an lvalue or
//:     rvalue of type (possibly `const`) `T`.  More precisely, `T` is
//:     `copy-insertable` into `X` means that the following expression is
//:     well-formed:
//:      `allocator_traits<A>::construct(m, p, v)`
//:
//: *move-assignable*: `T` provides an assignment operator that takes an rvalue
//:     of type (non-`const`) `T`.
//:
//: *copy-assignable*: `T` provides an assignment operator that takes an lvalue
//:     or rvalue of type (possibly `const`) `T`.
//:
//: *emplace-constructible*: `T` is `emplace-constructible` into `X` from
//:     `args` means that the following expression is well-formed:
//:
//:      `allocator_traits<A>::construct(m, p, args)`
//:
//: *erasable*: `T` provides a destructor.  More precisely, `T` is `erasable`
//:     from `X` means that the following expression is well-formed:
//:      `allocator_traits<A>::destroy(m, p)`
//:
//: *equality-comparable*: The type provides an equality-comparison operator
//:     that defines an equivalence relationship and is both reflexive and
//:     transitive.
//
///Memory Allocation
///-----------------
// The type supplied as a multimap's `ALLOCATOR` template parameter determines
// how that multimap will allocate memory.  The `multimap` template supports
// allocators meeting the requirements of the C++11 standard [17.6.3.5].  In
// addition, it supports scoped-allocators derived from the `bslma::Allocator`
// memory allocation protocol.  Clients intending to use `bslma`-style
// allocators should use the template's default `ALLOCATOR` type.  The default
// type for the `ALLOCATOR` template parameter, `bsl::allocator`, provides a
// C++11 standard-compatible adapter for a `bslma::Allocator` object.
//
///`bslma`-Style Allocators
/// - - - - - - - - - - - -
// If the (template parameter) type `ALLOCATOR` of a `multimap` instantiation
// is `bsl::allocator`, then objects of that multimap type will conform to the
// standard behavior of a `bslma`-allocator-enabled type.  Such a multimap
// accepts an optional `bslma::Allocator` argument at construction.  If the
// address of a `bslma::Allocator` object is explicitly supplied at
// construction, it is used to supply memory for the multimap throughout its
// lifetime; otherwise, the multimap will use the default allocator installed
// at the time of the multimap's construction (see `bslma_default`).  In
// addition to directly allocating memory from the indicated
// `bslma::Allocator`, a multimap supplies that allocator's address to the
// constructors of contained objects of the (template parameter) types `KEY`
// and `VALUE`, if respectively, the types define the
// `bslma::UsesBslmaAllocator` trait.
//
///Operations
///----------
// This section describes the run-time complexity of operations on instances
// of `multimap`:
// ```
// Legend
// ------
// 'K'             - (template parameter) type 'KEY' of the 'multimap'
// 'V'             - (template parameter) type 'VALUE' of the 'multimap'
// 'a', 'b'        - two distinct objects of type 'multimap<K, V>'
// 'rv'            - modifiable rvalue of type 'multimap<K, V>'
// 'n', 'm'        - number of elements in 'a' and 'b', respectively
// 'value_type'    - 'pair<const K, V>'
// 'c'             - comparator providing an ordering for objects of type 'K'
// 'al'            - STL-style memory allocator
// 'i1', 'i2'      - two iterators defining a sequence of 'value_type' objects
// 'k'             - object of type 'K'
// 'v'             - object of type 'V'
// 'vt'            - object of type 'value_type'
// 'rvt'           - modifiable rvalue of type 'value_type'
// 'p1', 'p2'      - two 'const_iterator's belonging to 'a'
// distance(i1,i2) - number of elements in the range '[i1 .. i2)'
//
// +----------------------------------------------------+--------------------+
// | Operation                                          | Complexity         |
// +====================================================+====================+
// | multimap<K, V> a;        (default construction)    | O[1]               |
// | multimap<K, V> a(al);                              |                    |
// | multimap<K, V> a(c, al);                           |                    |
// +----------------------------------------------------+--------------------+
// | multimap<K, V> a(rv);    (move construction)       | O[1] if 'a' and    |
// | multimap<K, V> a(rv, al);                          | 'rv' use the same  |
// |                                                    | allocator,         |
// |                                                    | O[n] otherwise     |
// +----------------------------------------------------+--------------------+
// | multimap<K, V> a(b);     (copy construction)       | O[n]               |
// | multimap<K, V> a(b, al);                           |                    |
// +----------------------------------------------------+--------------------+
// | multimap<K, V> a(i1, i2);                          | O[N] if [i1, i2)   |
// | multimap<K, V> a(i1, i2, al);                      | is sorted with     |
// | multimap<K, V> a(i1, i2, c, al);                   | 'a.value_comp()',  |
// |                                                    | O[N * log(N)]      |
// |                                                    | otherwise, where N |
// |                                                    | is distance(i1,i2) |
// +----------------------------------------------------+--------------------+
// | a.~multimap<K, V>();     (destruction)             | O[n]               |
// +----------------------------------------------------+--------------------+
// | a = rv;                  (move assignment)         | O[1] if 'a' and    |
// |                                                    | 'rv' use the same  |
// |                                                    | allocator,         |
// |                                                    | O[n] otherwise     |
// +----------------------------------------------------+--------------------+
// | a = b;                   (copy assignment)         | O[n]               |
// +----------------------------------------------------+--------------------+
// | a.begin(), a.end(), a.cbegin(), a.cend(),          | O[1]               |
// | a.rbegin(), a.rend(), a.crbegin(), a.crend()       |                    |
// +----------------------------------------------------+--------------------+
// | a == b, a != b                                     | O[n]               |
// +----------------------------------------------------+--------------------+
// | a < b, a <= b, a > b, a >= b                       | O[n]               |
// +----------------------------------------------------+--------------------+
// | a.swap(b), swap(a, b)                              | O[1] if 'a' and    |
// |                                                    | 'b' use the same   |
// |                                                    | allocator,         |
// |                                                    | O[n + m] otherwise |
// +----------------------------------------------------+--------------------+
// | a.size()                                           | O[1]               |
// +----------------------------------------------------+--------------------+
// | a.max_size()                                       | O[1]               |
// +----------------------------------------------------+--------------------+
// | a.empty()                                          | O[1]               |
// +----------------------------------------------------+--------------------+
// | get_allocator()                                    | O[1]               |
// +----------------------------------------------------+--------------------+
// | a.insert(vt)                                       | O[log(n)]          |
// | a.insert(rvt)                                      |                    |
// | a.emplace(Args&&...)                               |                    |
// +----------------------------------------------------+--------------------+
// | a.insert(p1, vt)                                   | amortized constant |
// | a.insert(p1, rvt)                                  | if the value is    |
// | a.emplace(p1, Args&&...)                           | inserted right     |
// |                                                    | before p1,         |
// |                                                    | O[log(n)]          |
// |                                                    | otherwise          |
// +----------------------------------------------------+--------------------+
// | a.insert(i1, i2)                                   | O[log(N) *         |
// |                                                    |   distance(i1,i2)] |
// |                                                    |                    |
// |                                                    | where N is         |
// |                                                    | n + distance(i1,i2)|
// +----------------------------------------------------+--------------------+
// | a.insert_range(rg)                                 | O[log(N) *         |
// |                                                    | ranges::           |
// |                                                    |      distance(rg)] |
// |                                                    |                    |
// |                                                    | where N is n +     |
// |                                                    | ranges::           |
// |                                                    |      distance(rg)] |
// +----------------------------------------------------+--------------------+
// | a.erase(p1)                                        | amortized constant |
// +----------------------------------------------------+--------------------+
// | a.erase(k)                                         | O[log(n) +         |
// |                                                    | a.count(k)]        |
// +----------------------------------------------------+--------------------+
// | a.erase(p1, p2)                                    | O[log(n) +         |
// |                                                    | distance(p1, p2)]  |
// +----------------------------------------------------+--------------------+
// | a.erase(p1, p2)                                    | O[log(n) +         |
// |                                                    | distance(p1, p2)]  |
// +----------------------------------------------------+--------------------+
// | a.clear()                                          | O[n]               |
// +----------------------------------------------------+--------------------+
// | a.contains(k)                                      | O[log(n)]          |
// +----------------------------------------------------+--------------------+
// | a.key_comp()                                       | O[1]               |
// +----------------------------------------------------+--------------------+
// | a.value_comp()                                     | O[1]               |
// +----------------------------------------------------+--------------------+
// | a.find(k)                                          | O[log(n)]          |
// +----------------------------------------------------+--------------------+
// | a.count(k)                                         | O[log(n) +         |
// |                                                    | a.count(k)]        |
// +----------------------------------------------------+--------------------+
// | a.lower_bound(k)                                   | O[log(n)]          |
// +----------------------------------------------------+--------------------+
// | a.upper_bound(k)                                   | O[log(n)]          |
// +----------------------------------------------------+--------------------+
// | a.equal_range(k)                                   | O[log(n)]          |
// +----------------------------------------------------+--------------------+
// ```
//
///Usage
///-----
// In this section we show intended use of this component.
//
///Example 1: Creating a Phone Book
/// - - - - - - - - - - - - - - - -
// In this example, we will define a class `PhoneBook`, that provides a mapping
// of names to phone numbers.  The `PhoneBook` class will be implemented using
// a `bsl::multimap`, and will supply manipulators, allowing a client to add or
// remove entries from the phone book, as well as accessors, allowing clients
// to efficiently lookup entries by name, and to iterate over the entries in
// the phone book in sorted order.
//
// Note that this example uses a type `string` that is based on the standard
// type `string` (see `bslstl_string`).  For the sake of brevity, the
// implementation of `string` is not explored here.
//
// First, we define an alias for a pair of `string` objects that we will use to
// represent names in the phone book:
// ```
// typedef bsl::pair<string, string> FirstAndLastName;
//     // This 'typedef' provides an alias for a pair of 'string' objects,
//     // whose 'first' and 'second' elements refer to the first and last
//     // names of a person, respectively.
// ```
// Then, we define a comparison functor for `FirstAndLastName` objects (note
// that this comparator is required because we intend for the last name to
// take precedence over the first name in the ordering of entries maintained
// by the phone book, which differs from the behavior supplied by `operator<`
// for `bsl::pair`):
// ```
// struct FirstAndLastNameLess {
//     // This 'struct' defines an ordering on 'FirstAndLastName' values,
//     // allowing them to be included in sorted containers such as
//     // 'bsl::multimap'.  Note that last name (the 'second' member of a
//     // 'FirstAndLastName' value) takes precedence over first name in the
//     // ordering defined by this functor.
//
//     bool operator()(const FirstAndLastName& lhs,
//                     const FirstAndLastName& rhs) const
//         // Return 'true' if the value of the specified 'lhs' is less than
//         // (ordered before) the value of the specified 'rhs', and 'false'
//         // otherwise.  The 'lhs' value is considered less than the 'rhs'
//         // value if the second value in the 'lhs' pair (the last name) is
//         // less than the second value in the 'rhs' pair or, if the second
//         // values are equal, if the first value in the 'lhs' pair (the
//         // first name) is less than the first value in the 'rhs' pair.
//     {
//         int cmp = std::strcmp(lhs.second.c_str(), rhs.second.c_str());
//         if (0 == cmp) {
//             cmp = std::strcmp(lhs.first.c_str(), rhs.first.c_str());
//         }
//         return cmp < 0;
//     }
// };
// ```
// Next, we define the public interface for `PhoneBook`:
// ```
// class PhoneBook {
//     // This class provides a mapping of a person's name to their phone
//     // number.  Names within a 'PhoneBook' are represented using a using
//     // 'FirstAndLastName' object, and phone numbers are represented using a
//     // 'bsls::Types::Uint64' value.
// ```
// Here, we create a type alias, `NameToNumberMap`, for a `bsl::multimap` that
// will serve as the data member for a `PhoneBook`.  A `NameToNumberMap` has
// keys of type `FirstAndLastName`, mapped-values of type
// `bsls::Types::Uint64`, and a comparator of type `FirstAndLastNameLess`.  We
// use the default `ALLOCATOR` template parameter as we intend to use
// `PhoneBook` with `bslma` style allocators:
// ```
//     // PRIVATE TYPES
//     typedef bsl::multimap<FirstAndLastName,
//                           bsls::Types::Uint64,
//                           FirstAndLastNameLess> NameToNumberMap;
//         // This 'typedef' is an alias for a mapping between names and phone
//         // numbers.
//
//     // DATA
//     NameToNumberMap d_nameToNumber;  // mapping of names to phone numbers
//
//     // FRIENDS
//     friend bool operator==(const PhoneBook& lhs, const PhoneBook& rhs);
//
//   public:
//     // PUBLIC TYPES
//     typedef bsls::Types::Uint64 PhoneNumber;
//         // This 'typedef' provides an alias for the type of an unsigned
//         // integers used to represent phone-numbers in a 'PhoneBook'.
//
//     typedef NameToNumberMap::const_iterator ConstIterator;
//         // This 'typedef' provides an alias for the type of an iterator
//         // providing non-modifiable access to the entries in a 'PhoneBook'.
//
//     // CREATORS
//     PhoneBook(bslma::Allocator *basicAllocator = 0);
//         // Create an empty 'PhoneBook' object.  Optionally specify a
//         // 'basicAllocator' used to supply memory.  If 'basicAllocator' is
//         // 0, the currently installed default allocator is used.
//
//     PhoneBook(const PhoneBook&  original,
//               bslma::Allocator  *basicAllocator = 0);
//         // Create a 'PhoneBook' object having the same value as the
//         // specified 'original' object.  Optionally specify a
//         // 'basicAllocator' used to supply memory.  If 'basicAllocator' is
//         // 0, the currently installed default allocator is used.
//
//     //! ~PhoneBook() = default;
//         // Destroy this object.
//
//     // MANIPULATORS
//     PhoneBook& operator=(const PhoneBook& rhs);
//         // Assign to this object the value of the specified 'rhs' object,
//         // and return a reference providing modifiable access to this
//         // object.
//
//     void addEntry(const FirstAndLastName& name, PhoneNumber number);
//         // Add an entry to this phone book having the specified 'name' and
//         // 'number'.  The behavior is undefined unless 'name.first' and
//         // 'name.end' are non-empty strings.
//
//     int removeEntry(const FirstAndLastName& name, PhoneNumber number);
//         // Remove the entries from this phone book having the specified
//         // 'name' and 'number', if they exists, and return the number of
//         // removed entries; otherwise, return 0 with no other effects.
//
//     // ACCESSORS
//     bsl::pair<ConstIterator, ConstIterator> lookupByName(
//                                        const FirstAndLastName& name) const;
//         // Return a pair of iterators to the ordered sequence of entries
//         // held in this phone book having the specified 'name', where the
//         // first iterator is position at the start of the sequence, and the
//         // second is positioned one past the last entry in the sequence.
//         // If 'name' does not exist in this phone book, then the two
//         // returned iterators will have the same value.
//
//     ConstIterator begin() const;
//         // Return an iterator providing non-modifiable access to the first
//         // entry in the ordered sequence of entries held in this phone
//         // book, or the past-the-end iterator if this phone book is empty.
//
//     ConstIterator end() const;
//         // Return an iterator providing non-modifiable access to the
//         // past-the-end entry in the ordered sequence of entries maintained
//         // by this phone book.
//
//     size_t numEntries() const;
//         // Return the number of entries contained in this phone book.
// };
// ```
// Then, we declare the free operators for `PhoneBook`:
// ```
// inline
// bool operator==(const PhoneBook& lhs, const PhoneBook& rhs);
//     // Return 'true' if the specified 'lhs' and 'rhs' objects have the same
//     // value, and 'false' otherwise.  Two 'PhoneBook' objects have the
//     // same value if they have the same number of entries, and each
//     // corresponding entry, in their respective ordered sequence of
//     // entries, is the same.
//
// inline
// bool operator!=(const PhoneBook& lhs, const PhoneBook& rhs);
//     // Return 'true' if the specified 'lhs' and 'rhs' objects do not have
//     // the same value, and 'false' otherwise.  Two 'PhoneBook' objects do
//     // not have the same value if they either differ in their number of
//     // contained entries, or if any of the corresponding entries, in their
//     // respective ordered sequences of entries, is not the same.
// ```
// Now, we define the implementations methods of the `PhoneBook` class:
// ```
// // CREATORS
// inline
// PhoneBook::PhoneBook(bslma::Allocator *basicAllocator)
// : d_nameToNumber(FirstAndLastNameLess(), basicAllocator)
// {
// }
// ```
// Notice that, on construction, we pass the contained `bsl::multimap`
// (`d_nameToNumber`), a default constructed `FirstAndLastNameLess` object that
// it will use to perform comparisons, and the allocator supplied to
// `PhoneBook` at construction'.
// ```
// inline
// PhoneBook::PhoneBook(const PhoneBook&   original,
//                      bslma::Allocator  *basicAllocator)
// : d_nameToNumber(original.d_nameToNumber, basicAllocator)
// {
// }
//
// // MANIPULATORS
// inline
// PhoneBook& PhoneBook::operator=(const PhoneBook& rhs)
// {
//     d_nameToNumber = rhs.d_nameToNumber;
//     return *this;
// }
//
// inline
// void PhoneBook::addEntry(const FirstAndLastName& name, PhoneNumber number)
// {
//     BSLS_ASSERT(!name.first.empty());
//     BSLS_ASSERT(!name.second.empty());
//
//     d_nameToNumber.insert(NameToNumberMap::value_type(name, number));
// }
//
// inline
// int PhoneBook::removeEntry(const FirstAndLastName& name,
//                            PhoneNumber             number)
// {
//     bsl::pair<NameToNumberMap::iterator, NameToNumberMap::iterator> range =
//                                           d_nameToNumber.equal_range(name);
//
//     NameToNumberMap::iterator it = range.first;
//
//     int numRemovedEntries = 0;
//
//     while (it != range.second) {
//         if (it->second == number) {
//             it = d_nameToNumber.erase(it);
//             ++numRemovedEntries;
//         }
//         else {
//             ++it;
//         }
//     }
//
//     return numRemovedEntries;
// }
//
// // ACCESSORS
// inline
// bsl::pair<PhoneBook::ConstIterator, PhoneBook::ConstIterator>
// PhoneBook::lookupByName(const FirstAndLastName&  name) const
// {
//     return d_nameToNumber.equal_range(name);
// }
//
// inline
// PhoneBook::ConstIterator PhoneBook::begin() const
// {
//     return d_nameToNumber.begin();
// }
//
// inline
// PhoneBook::ConstIterator PhoneBook::end() const
// {
//     return d_nameToNumber.end();
// }
//
// inline
// size_t PhoneBook::numEntries() const
// {
//     return d_nameToNumber.size();
// }
// ```
// Finally, we implement the free operators for `PhoneBook`:
// ```
// inline
// bool operator==(const PhoneBook& lhs, const PhoneBook& rhs)
// {
//     return lhs.d_nameToNumber == rhs.d_nameToNumber;
// }
//
// inline
// bool operator!=(const PhoneBook& lhs, const PhoneBook& rhs)
// {
//     return !(lhs == rhs);
// }
// ```

#include <bslscm_version.h>

#include <bslstl_algorithm.h>
#include <bslstl_iterator.h>
#include <bslstl_iteratorutil.h>
#include <bslstl_mapcomparator.h>
#include <bslstl_pair.h>
#include <bslstl_ranges.h>
#include <bslstl_stdexceptutil.h>
#include <bslstl_treeiterator.h>
#include <bslstl_treenode.h>
#include <bslstl_treenodepool.h>

#include <bslalg_rangecompare.h>
#include <bslalg_rbtreeanchor.h>
#include <bslalg_rbtreenode.h>
#include <bslalg_rbtreeutil.h>
#include <bslalg_swaputil.h>
#include <bslalg_synththreewayutil.h>
#include <bslalg_typetraithasstliterators.h>

#include <bslma_isstdallocator.h>
#include <bslma_bslallocator.h>
#include <bslma_usesbslmaallocator.h>

#include <bslmf_containercompatiblerange.h>
#include <bslmf_enableif.h>
#include <bslmf_isconvertible.h>
#include <bslmf_istransparentpredicate.h>
#include <bslmf_movableref.h>
#include <bslmf_typeidentity.h>
#include <bslmf_util.h>    // 'forward(V)'

#include <bsls_assert.h>
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
#include <bsls_performancehint.h>
#include <bsls_platform.h>
#include <bsls_util.h>     // 'forward<T>(V)'

#include <functional>

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
# include <initializer_list>
#endif

#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bsls_nativestd.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES

#ifdef BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER
#include <type_traits>  // 'std::is_constructible'
    #ifndef BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES
    #error Rvalue references curiously absent despite native 'type_traits'.
    #endif
#endif

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
# define BSLSTL_MULTIMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(R, T) \
                  requires ::BloombergLP::bslmf::ContainerCompatibleRange<R, T>
#else
# define BSLSTL_MULTIMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(R, T)
#endif

#if BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
// clang-format off
// Include version that can be compiled with C++03
// Generated on Mon Jan 13 08:31:39 2025
// Command line: sim_cpp11_features.pl bslstl_multimap.h

# define COMPILING_BSLSTL_MULTIMAP_H
# include <bslstl_multimap_cpp03.h>
# undef COMPILING_BSLSTL_MULTIMAP_H

// clang-format on
#else

namespace bsl {

                             // ==============
                             // class multimap
                             // ==============

/// This class template implements a value-semantic container type holding
/// an ordered sequence of key-value pairs having possibly duplicate keys
/// that provide a mapping from keys (of the template parameter type, `KEY`)
/// to their associated values (of another template parameter type,
/// `VALUE`).
///
/// This class:
/// * supports a complete set of *value-semantic* operations
///   - except for BDEX serialization
/// * is *exception-neutral*
/// * is *alias-safe*
/// * is `const` *thread-safe*
/// For terminology see {`bsldoc_glossary`}.
template <class KEY,
          class VALUE,
          class COMPARATOR = std::less<KEY>,
          class ALLOCATOR  = allocator<pair<const KEY, VALUE> > >
class multimap {

    // PRIVATE TYPES

    /// This typedef is an alias for the type of key-value pair objects
    /// maintained by this multimap.
    typedef pair<const KEY, VALUE>                             ValueType;

    /// This typedef is an alias for the comparator used internally by this
    /// multimap.
    typedef BloombergLP::bslstl::MapComparator<KEY, VALUE, COMPARATOR>
                                                               Comparator;

    /// This typedef is an alias for the type of nodes held by the tree (of
    /// nodes) used to implement this multimap.
    typedef BloombergLP::bslstl::TreeNode<ValueType>           Node;

    /// This typedef is an alias for the factory type used to create and
    /// destroy `Node` objects.
    typedef BloombergLP::bslstl::TreeNodePool<ValueType, ALLOCATOR>
                                                               NodeFactory;

    /// This typedef is an alias for the allocator traits type associated
    /// with this container.
    typedef typename bsl::allocator_traits<ALLOCATOR>          AllocatorTraits;

    /// This typedef is a convenient alias for the utility associated with
    /// movable references.
    typedef BloombergLP::bslmf::MovableRefUtil                 MoveUtil;

    /// This class is a wrapper around the comparator and allocator data
    /// members.  It takes advantage of the empty-base optimization (EBO) so
    /// that if the comparator is stateless, it takes up no space.
    ///
    /// TBD: This class should eventually be replaced by the use of a
    /// general EBO-enabled component that provides a `pair`-like interface
    /// or a `tuple`.
    class DataWrapper : public Comparator {

        // DATA
        NodeFactory d_pool;  // pool of 'Node' objects

      private:
        // NOT IMPLEMENTED
        DataWrapper(const DataWrapper&);
        DataWrapper& operator=(const DataWrapper&);

      public:
        // CREATORS

        /// Create a data wrapper using a copy of the specified `comparator`
        /// to order key-value pairs and a copy of the specified
        /// `basicAllocator` to supply memory.
        DataWrapper(const COMPARATOR& comparator,
                    const ALLOCATOR&  basicAllocator);

        /// Create a data wrapper initialized to the contents of the `pool`
        /// associated with the specified `original` data wrapper.  The
        /// comparator and allocator associated with `original` are
        /// propagated to the new data wrapper.  `original` is left in a
        /// valid but unspecified state.
        DataWrapper(
              BloombergLP::bslmf::MovableRef<DataWrapper> original);// IMPLICIT

        // MANIPULATORS

        /// Return a reference providing modifiable access to the node
        /// factory associated with this data wrapper.
        NodeFactory& nodeFactory();

        // ACCESSORS

        /// Return a reference providing non-modifiable access to the node
        /// factory associated with this data wrapper.
        const NodeFactory& nodeFactory() const;
    };

    // DATA
    DataWrapper                       d_compAndAlloc;
                                               // comparator and pool of 'Node'
                                               // objects

    BloombergLP::bslalg::RbTreeAnchor d_tree;  // balanced tree of 'Node'
                                               // objects

  public:
    // PUBLIC TYPES
    typedef KEY                                        key_type;
    typedef VALUE                                      mapped_type;
    typedef pair<const KEY, VALUE>                     value_type;
    typedef COMPARATOR                                 key_compare;
    typedef ALLOCATOR                                  allocator_type;
    typedef value_type&                                reference;
    typedef const value_type&                          const_reference;

    typedef typename AllocatorTraits::size_type        size_type;
    typedef typename AllocatorTraits::difference_type  difference_type;
    typedef typename AllocatorTraits::pointer          pointer;
    typedef typename AllocatorTraits::const_pointer    const_pointer;

    typedef BloombergLP::bslstl::TreeIterator<value_type,
                                              Node,
                                              difference_type> iterator;

    typedef BloombergLP::bslstl::TreeIterator<const value_type,
                                              Node,
                                              difference_type> const_iterator;

    typedef bsl::reverse_iterator<iterator>            reverse_iterator;
    typedef bsl::reverse_iterator<const_iterator>      const_reverse_iterator;

    /// This nested class defines a mechanism for comparing two objects of
    /// `value_type` by adapting an object of (template parameter) type
    /// `COMPARATOR`, which compares two objects of (template parameter)
    /// type `KEY` .  Note that this class exactly matches its definition in
    /// the C++11 standard [23.4.4.1]; otherwise, we would have implemented
    /// it as a separate component-local class.
    class value_compare {

        // FRIENDS
        friend class multimap;

      protected:
        // PROTECTED DATA
        COMPARATOR comp;  // we would not have elected to make this data
                          // member 'protected'

        // PROTECTED CREATORS

        /// Create a `value_compare` object that uses the specified
        /// `comparator`.
        value_compare(COMPARATOR comparator);                       // IMPLICIT

      public:
        // PUBLIC TYPES

        /// This `typedef` is an alias for the result type of a call to the
        /// overload of `operator()` (the comparison function) provided by a
        /// `multimap::value_compare` object.
        typedef bool result_type;

        /// This `typedef` is an alias for the type of the first parameter
        /// of the overload of `operator()` (the comparison function)
        /// provided by a `multimap::value_compare` object.
        typedef value_type first_argument_type;

        /// This `typedef` is an alias for the type of the second parameter
        /// of the overload of `operator()` (the comparison function)
        /// provided by a `multimap::value_compare` object.
        typedef value_type second_argument_type;

        // CREATORS
        //! value_compare(const value_compare& original) = default;
            // Create a 'value_compare' object having the same value as the
            // specified 'original' object.

        //! ~value_compare() = default;
            // Destroy this object.

        // MANIPULATORS
        //! value_compare& operator=(const value_compare& rhs) = default;
            // Assign to this object the value of the specified 'rhs' object,
            // and return a reference providing modifiable access to this
            // object.

        // ACCESSORS

        /// Return `true` if the specified `x` object is ordered before the
        /// specified `y` object, as determined by the comparator supplied
        /// at construction, and `false` otherwise.
        bool operator()(const value_type& x, const value_type& y) const;
    };

  private:
    // PRIVATE CLASS METHODS

    /// Return an address providing modifiable access to the specified
    /// `node`.  The behavior is undefined unless `node` is the address of a
    /// `Node` object.
    static Node *toNode(BloombergLP::bslalg::RbTreeNode *node);

    /// Return an address providing non-modifiable access to the specified
    /// `node`.  The behavior is undefined unless `node` is the address of a
    /// `Node` object.
    static const Node *toNode(const BloombergLP::bslalg::RbTreeNode *node);

    // PRIVATE MANIPULATORS

    /// Return a reference providing modifiable access to the comparator for
    /// this multimap.
    Comparator& comparator();

    /// Return a reference providing modifiable access to the node allocator
    /// for this multimap.
    NodeFactory& nodeFactory();

    /// Efficiently exchange the value, comparator, and allocator of this
    /// object with the value, comparator, and allocator of the specified
    /// `other` object.  This method provides the no-throw exception-safety
    /// guarantee, *unless* swapping the (user-supplied) comparator or
    /// allocator objects can throw.
    void quickSwapExchangeAllocators(multimap& other);

    /// Efficiently exchange the value and comparator of this object with
    /// the value and comparator of the specified `other` object.  This
    /// method provides the no-throw exception-safety guarantee, *unless*
    /// swapping the (user-supplied) comparator objects can throw.  The
    /// behavior is undefined unless this object was created with the same
    /// allocator as `other`.
    void quickSwapRetainAllocators(multimap& other);

    /// Insert the values between the specified `first` and `last` into an
    /// initially empty multimap.  If sorted, directly place each value in its
    /// proper position. If an out of order value is detected, revert to
    /// normal insertion.
    template <class INPUT_ITERATOR, class SENTINEL>
    void constructFromRange(INPUT_ITERATOR first, SENTINEL last);

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)

    /// Insert the values between the specified `first` and `last` into an
    /// initially empty multimap.  The specified 'numElements` is used to
    /// improve performance.  If sorted, directly place each value in its
    /// proper position.  If an out of order value is detected, revert to
    /// normal insertion.  The behavior is undefined if the iterators support
    /// the calculation of distance and `numElements` is not the distance
    /// from `first` to `last`.
    template <class INPUT_ITERATOR, class SENTINEL>
    void constructFromRange(INPUT_ITERATOR first,
                            SENTINEL       last,
                            size_t         numElements);
#endif

    // Insert the values between `first` and `last` into this multimap.
    template <class INPUT_ITERATOR, class SENTINEL>
    void insertFromRange(INPUT_ITERATOR first,
                         SENTINEL       last);

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)

    /// Insert the values between the specified `first` and `last` into this
    /// multimap. The specified `numElements` is used to improve performance.
    /// The behavior is undefined if the iterators support the calculation
    /// of distance and `numElements` is not the distance from `first` to
    /// `last`.
    template <class INPUT_ITERATOR, class SENTINEL>
    void insertFromRange(INPUT_ITERATOR first,
                         SENTINEL       last,
                         size_t         numElements);
#endif

    // PRIVATE ACCESSORS

    /// Return a reference providing non-modifiable access to the comparator
    /// for this multimap.
    const Comparator& comparator() const;

    /// Return a reference providing non-modifiable access to the node
    /// allocator for this multimap.
    const NodeFactory& nodeFactory() const;

  public:
    // CREATORS

    /// Create an empty multimap.  Optionally specify a `comparator` used to
    /// order key-value pairs contained in this object.  If `comparator` is
    /// not supplied, a default-constructed object of the (template
    /// parameter) type `COMPARATOR` is used.  Optionally specify a
    /// `basicAllocator` used to supply memory.  If `basicAllocator` is not
    /// supplied, a default-constructed object of the (template parameter)
    /// type `ALLOCATOR` is used.  If the type `ALLOCATOR` is
    /// `bsl::allocator` (the default), then `basicAllocator`, if supplied,
    /// shall be convertible to `bslma::Allocator *`.  If the type
    /// `ALLOCATOR` is `bsl::allocator` and `basicAllocator` is not
    /// supplied, the currently installed default allocator is used.
    multimap();
    explicit multimap(const COMPARATOR& comparator,
                      const ALLOCATOR&  basicAllocator = ALLOCATOR())
    : d_compAndAlloc(comparator, basicAllocator)
    , d_tree()
    {
        // The implementation is placed here in the class definition to work
        // around an AIX compiler bug, where the constructor can fail to
        // compile because it is unable to find the definition of the default
        // argument.  This occurs when a parameterized class wraps around the
        // container and the comparator is defined after the new class.
    }

    /// Create an empty multimap that uses the specified `basicAllocator` to
    /// supply memory.  Use a default-constructed object of the (template
    /// parameter) type `COMPARATOR` to order the key-value pairs contained
    /// in this multimap.  Note that a `bslma::Allocator *` can be supplied
    /// for `basicAllocator` if the (template parameter) `ALLOCATOR` is
    /// `bsl::allocator` (the default).
    explicit multimap(const ALLOCATOR& basicAllocator);

    /// Create a multimap having the same value as the specified `original`
    /// object.  Use a copy of `original.key_comp()` to order the key-value
    /// pairs contained in this multimap.  Use the allocator returned by
    /// 'bsl::allocator_traits<ALLOCATOR>::
    /// select_on_container_copy_construction(original.get_allocator())' to
    /// allocate memory.  This method requires that the (template parameter)
    /// types `KEY` and `VALUE` both be `copy-insertable` into this multimap
    /// (see {Requirements on `KEY` and `VALUE`}).
    multimap(const multimap& original);

    /// Create a multimap having the same value as the specified `original`
    /// object by moving (in constant time) the contents of `original` to
    /// the new multimap.  Use a copy of `original.key_comp()` to order the
    /// key-value pairs contained in this multimap.  The allocator
    /// associated with `original` is propagated for use in the
    /// newly-created multimap.  `original` is left in a valid but
    /// unspecified state.
    multimap(BloombergLP::bslmf::MovableRef<multimap> original);    // IMPLICIT

    /// Create a multimap having the same value as the specified `original`
    /// object that uses the specified `basicAllocator` to supply memory.
    /// Use a copy of `original.key_comp()` to order the key-value pairs
    /// contained in this multimap.  This method requires that the (template
    /// parameter) types `KEY` and `VALUE` both be `copy-insertable` into
    /// this multimap (see {Requirements on `KEY` and `VALUE`}).  Note that
    /// a `bslma::Allocator *` can be supplied for `basicAllocator` if the
    /// (template parameter) `ALLOCATOR` is `bsl::allocator` (the default).
    multimap(const multimap&                                original,
             const typename type_identity<ALLOCATOR>::type& basicAllocator);

    /// Create a multimap having the same value as the specified `original`
    /// object that uses the specified `basicAllocator` to supply memory.
    /// The contents of `original` are moved (in constant time) to the new
    /// multimap if `basicAllocator == original.get_allocator()`, and are
    /// move-inserted (in linear time) using `basicAllocator` otherwise.
    /// `original` is left in a valid but unspecified state.  Use a copy of
    /// `original.key_comp()` to order the key-value pairs contained in this
    /// multimap.  This method requires that the (template parameter) types
    /// `KEY` and `VALUE` both be `move-insertable` into this multimap (see
    /// {Requirements on `KEY` and `VALUE`}).  Note that a 'bslma::Allocator
    /// *` can be supplied for `basicAllocator' if the (template parameter)
    /// `ALLOCATOR` is `bsl::allocator` (the default).
    multimap(BloombergLP::bslmf::MovableRef<multimap>       original,
             const typename type_identity<ALLOCATOR>::type& basicAllocator);

    /// Create a multimap, and insert each `value_type` object in the
    /// sequence starting at the specified `first` element, and ending
    /// immediately before the specified `last` element.  Optionally specify
    /// a `comparator` used to order key-value pairs contained in this
    /// object.  If `comparator` is not supplied, a default-constructed
    /// object of the (template parameter) type `COMPARATOR` is used.
    /// Optionally specify a `basicAllocator` used to supply memory.  If
    /// `basicAllocator` is not supplied, a default-constructed object of
    /// the (template parameter) type `ALLOCATOR` is used.  If the type
    /// `ALLOCATOR` is `bsl::allocator` (the default), then
    /// `basicAllocator`, if supplied, shall be convertible to
    /// `bslma::Allocator *`.  If the type `ALLOCATOR` is `bsl::allocator`
    /// and `basicAllocator` is not supplied, the currently installed
    /// default allocator is used.  If the sequence `first` to `last` is
    /// ordered according to `comparator`, then this operation has `O[N]`
    /// complexity, where `N` is the number of elements between `first` and
    /// `last`; otherwise, this operation has `O[N * log(N)]` complexity.
    /// The (template parameter) type `INPUT_ITERATOR` shall meet the
    /// requirements of an input iterator defined in the C++11 standard
    /// [24.2.3] providing access to values of a type convertible to
    /// `value_type`, and `value_type` must be `emplace-constructible` from
    /// `*i` into this multimap, where `i` is a dereferenceable iterator in
    /// the range `[first .. last)` (see {Requirements on `KEY` and
    /// `VALUE`}).  The behavior is undefined unless `first` and `last`
    /// refer to a sequence of valid values where `first` is at a position
    /// at or before `last`.
    template <class INPUT_ITERATOR>
    multimap(INPUT_ITERATOR    first,
             INPUT_ITERATOR    last,
             const COMPARATOR& comparator     = COMPARATOR(),
             const ALLOCATOR&  basicAllocator = ALLOCATOR());
    template <class INPUT_ITERATOR>
    multimap(INPUT_ITERATOR    first,
             INPUT_ITERATOR    last,
             const ALLOCATOR&  basicAllocator);

    /// Create a multimap having the (`value_type`) values obtained from the
    /// specified `range`.  Optionally specify a `comparator` used to order
    /// key-value pairs contained in this object.  If `comparator` is not
    /// supplied, a default-constructed object of the (template parameter) type
    /// `COMPARATOR` is used.  Optionally specify a `basicAllocator` used to
    /// supply memory.  If `basicAllocator` is not supplied, a
    /// default-constructed object of the (template parameter) type `ALLOCATOR`
    /// is used.  If the type `ALLOCATOR` is `bsl::allocator` (the default),
    /// then `basicAllocator`, if supplied, shall be convertible to
    /// `bslma::Allocator *`.  If the type `ALLOCATOR` is `bsl::allocator` and
    /// `basicAllocator` is not supplied, the currently installed default
    /// allocator is used.  If values obtained from `range` are ordered
    /// according to `comparator`, then this operation has `O[N]` complexity,
    /// where `N` is the number of values in the `range`; otherwise, this
    /// operation has `O[N * log(N)]` complexity.  Note that `RANGE` must meet
    /// the requirements of an input range and the values from `range` must
    /// have a type matching or convertible to `value_type`.
    template <class RANGE>
    BSLSTL_MULTIMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    multimap(
        bsl::from_range_t                        ,
        BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
        const COMPARATOR&                        comparator     = COMPARATOR(),
        const ALLOCATOR&                         basicAllocator = ALLOCATOR())
    : d_compAndAlloc(comparator, basicAllocator)
    , d_tree()
    {
        // Defined inline to avoid Windows errors.

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
        if constexpr (std::ranges::sized_range<RANGE>) {
            constructFromRange(bsl::ranges::begin(range),
                               bsl::ranges::end  (range),
                               bsl::ranges::size (range));
        } else // ...
#endif
        {
            constructFromRange(bsl::ranges::begin(range),
                               bsl::ranges::end  (range));
        }
    }

    template <class RANGE>
    BSLSTL_MULTIMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    multimap(from_range_t                             ,
             BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range,
             const ALLOCATOR&                         basicAllocator)
    : d_compAndAlloc(COMPARATOR(), basicAllocator)
    , d_tree()
    {
        // Defined inline to avoid Windows errors.

        multimap other(bsl::from_range,
                       range,
                       COMPARATOR(),
                       nodeFactory().allocator());
        quickSwapRetainAllocators(other);
    }

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
    /// Create a multimap and insert each `value_type` object in the
    /// specified `values` initializer list.  Optionally specify a
    /// `comparator` used to order keys contained in this object.  If
    /// `comparator` is not supplied, a default-constructed object of the
    /// (template parameter) type `COMPARATOR` is used.  Optionally specify
    /// a `basicAllocator` used to supply memory.  If `basicAllocator` is
    /// not supplied, a default-constructed object of the (template
    /// parameter) type `ALLOCATOR` is used.  If the type `ALLOCATOR` is
    /// `bsl::allocator` (the default), then `basicAllocator`, if supplied,
    /// shall be convertible to `bslma::Allocator *`.  If the type
    /// `ALLOCATOR` is `bsl::allocator` and `basicAllocator` is not
    /// supplied, the currently installed default allocator is used.  If
    /// `values` is ordered according to `comparator`, then this operation
    /// has `O[N]` complexity, where `N` is the number of elements in
    /// `values`; otherwise, this operation has `O[N * log(N)]` complexity.
    /// This method requires that the (template parameter) types `KEY` and
    /// `VALUE` both be `copy-insertable` into this multimap (see
    /// {Requirements on `KEY` and `VALUE`}).
    multimap(std::initializer_list<value_type> values,
             const COMPARATOR&                 comparator     = COMPARATOR(),
             const ALLOCATOR&                  basicAllocator = ALLOCATOR());
    multimap(std::initializer_list<value_type> values,
             const ALLOCATOR&                  basicAllocator);
#endif

    /// Destroy this object.
    ~multimap();

    // MANIPULATORS

    /// Assign to this object the value and comparator of the specified
    /// `rhs` object, propagate to this object the allocator of `rhs` if the
    /// `ALLOCATOR` type has trait `propagate_on_container_copy_assignment`,
    /// and return a reference providing modifiable access to this object.
    /// If an exception is thrown, `*this` is left in a valid but
    /// unspecified state.  This method requires that the (template
    /// parameter) types `KEY` and `VALUE` both be `copy-assignable` and
    /// `copy-insertable` into this multimap (see {Requirements on `KEY` and
    /// `VALUE`}).
    multimap& operator=(const multimap& rhs);

    multimap& operator=(BloombergLP::bslmf::MovableRef<multimap> rhs)
        BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                           AllocatorTraits::is_always_equal::value &&
                           std::is_nothrow_move_assignable<COMPARATOR>::value);
        // Assign to this object the value and comparator of the specified
        // 'rhs' object, propagate to this object the allocator of 'rhs' if the
        // 'ALLOCATOR' type has trait 'propagate_on_container_move_assignment',
        // and return a reference providing modifiable access to this object.
        // The contents of 'rhs' are moved (in constant time) to this multimap
        // if 'get_allocator() == rhs.get_allocator()' (after accounting for
        // the aforementioned trait); otherwise, all elements in this multimap
        // are either destroyed or move-assigned to and each additional element
        // in 'rhs' is move-inserted into this multimap.  'rhs' is left in a
        // valid but unspecified state, and if an exception is thrown, '*this'
        // is left in a valid but unspecified state.  This method requires that
        // the (template parameter) types 'KEY' and 'VALUE' both be
        // 'move-assignable' and 'move-insertable' into this multimap (see
        // {Requirements on 'KEY' and 'VALUE'}).

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
    /// Assign to this object the value resulting from first clearing this
    /// multimap and then inserting each `value_type` object in the
    /// specified `values` initializer list, and return a reference
    /// providing modifiable access to this object.  This method requires
    /// that the (template parameter) types `KEY` and `VALUE` both be
    /// `copy-insertable` into this multimap (see {Requirements on `KEY` and
    /// `VALUE`}).
    multimap& operator=(std::initializer_list<value_type> values);
#endif

    /// Return an iterator providing modifiable access to the first
    /// `value_type` object in the ordered sequence of `value_type` objects
    /// maintained by this multimap, or the `end` iterator if this multimap
    /// is empty.
    iterator begin() BSLS_KEYWORD_NOEXCEPT;

    /// Return an iterator providing modifiable access to the past-the-end
    /// element in the ordered sequence of `value_type` objects maintained
    /// by this multimap.
    iterator end() BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing modifiable access to the last
    /// `value_type` object in the ordered sequence of `value_type` objects
    /// maintained by this multimap, or `rend` if this multimap is empty.
    reverse_iterator rbegin() BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing modifiable access to the
    /// prior-to-the-beginning element in the ordered sequence of
    /// `value_type` objects maintained by this multimap.
    reverse_iterator rend() BSLS_KEYWORD_NOEXCEPT;

    /// Insert the specified `value` into this multimap.  If a range
    /// containing elements equivalent to `value` already exists, insert the
    /// `value` at the end of that range.  Return an iterator referring to
    /// the newly inserted `value_type` object.  This method requires that
    /// the (template parameter) types `KEY` and `VALUE` both be
    /// `copy-insertable` into this multimap (see {Requirements on `KEY` and
    /// `VALUE`}).
    iterator insert(const value_type& value);

#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
    template <class ALT_VALUE_TYPE>
    iterator
#elif !defined(BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER)
    template <class ALT_VALUE_TYPE>
    typename enable_if<is_convertible<ALT_VALUE_TYPE, value_type>::value,
                       iterator>::type
#else
    /// Insert into this multimap a `value_type` object created from the
    /// specified `value`.  If a range containing elements equivalent to
    /// `value_type` object already exists, insert the `value_type` object
    /// at the end of that range.  Return an iterator referring to the newly
    /// inserted `value_type` object.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` both be
    /// `move-insertable` into this multimap (see {Requirements on `KEY` and
    /// `VALUE`}), and the `value_type` be constructible from the (template
    /// parameter) `ALT_VALUE_TYPE`.
    template <class ALT_VALUE_TYPE>
    typename enable_if<std::is_constructible<value_type,
                                             ALT_VALUE_TYPE&&>::value,
                       iterator>::type
#endif
    insert(BSLS_COMPILERFEATURES_FORWARD_REF(ALT_VALUE_TYPE) value)
    {
        // Note that some compilers fail when this method is defined
        // out-of-line.

        return emplace(BSLS_COMPILERFEATURES_FORWARD(ALT_VALUE_TYPE, value));
    }

    /// Insert the specified `value` into this multimap (in amortized
    /// constant time if the specified `hint` is a valid immediate successor
    /// to the key of `value`).  Return an iterator referring to the newly
    /// inserted `value_type` object.  If `hint` is not a valid immediate
    /// successor to the key of `value`, this operation has `O[log(N)]`
    /// complexity, where `N` is the size of this multimap.  This method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `copy-insertable` into this multimap (see {Requirements on `KEY`
    /// and `VALUE`}).  The behavior is undefined unless `hint` is an
    /// iterator in the range `[begin() .. end()]` (both endpoints
    /// included).
    iterator insert(const_iterator hint, const value_type& value);

#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
    template <class ALT_VALUE_TYPE>
    iterator
#elif !defined(BSLS_COMPILERFEATURES_SUPPORT_TRAITS_HEADER)
    template <class ALT_VALUE_TYPE>
    typename enable_if<is_convertible<ALT_VALUE_TYPE, value_type>::value,
                       iterator>::type
#else
    /// Insert into this multimap a `value_type` object created from the
    /// specified `value` (in amortized constant time if the specified
    /// `hint` is a valid immediate successor to the object created from
    /// `value`).  Return an iterator referring to the newly inserted
    /// `value_type` object in this multimap.  If `hint` is not a valid
    /// immediate successor to the object created from `value`, this
    /// operation has `O[log(N)]` complexity, where `N` is the size of this
    /// multimap.  This method requires that the (template parameter) types
    /// `KEY` and `VALUE` both be `move-insertable` into this multimap (see
    /// {Requirements on `KEY` and `VALUE`}), and the `value_type` be
    /// constructible from the (template parameter) `ALT_VALUE_TYPE`.  The
    /// behavior is undefined unless `hint` is an iterator in the range
    /// `[begin() .. end()]` (both endpoints included).
    template <class ALT_VALUE_TYPE>
    typename enable_if<std::is_constructible<value_type,
                                             ALT_VALUE_TYPE&&>::value,
                       iterator>::type
#endif
    insert(const_iterator                                    hint,
           BSLS_COMPILERFEATURES_FORWARD_REF(ALT_VALUE_TYPE) value)
    {
        // Note that some compilers fail when this method is defined
        // out-of-line.

        return emplace_hint(hint,
                        BSLS_COMPILERFEATURES_FORWARD(ALT_VALUE_TYPE, value));
    }

    /// Insert into this multimap the value of each `value_type` object in
    /// the range starting at the specified `first` iterator and ending
    /// immediately before the specified `last` iterator.  The (template
    /// parameter) type `INPUT_ITERATOR` shall meet the requirements of an
    /// input iterator defined in the C++11 standard [24.2.3] providing
    /// access to values of a type convertible to `value_type`, and
    /// `value_type` must be `emplace-constructible` from `*i` into this
    /// multimap, where `i` is a dereferenceable iterator in the range
    /// `[first .. last)` (see {Requirements on `KEY` and `VALUE`}).  The
    /// behavior is undefined unless `first` and `last` refer to a sequence
    /// of valid values where `first` is at a position at or before `last`.
    template <class INPUT_ITERATOR>
    void insert(INPUT_ITERATOR first, INPUT_ITERATOR last);

    /// Insert into this multimap the value of each `value_type` object in the
    /// specified `range`.  The (template parameter) type `RANGE` must meet the
    /// requirements of the C++20 standard [ranges] providing access to values
    /// of a type convertible to `value_type`, and `value_type` must be
    /// `emplace-constructible` from `*i` into this multimap, where `i` is a
    /// dereferenceable iterator obtained from `range` (see {Requirements on
    /// `KEY` and `VALUE`}).  The behavior is undefined if `range` overlaps
    /// this multimap.
    template <class RANGE>
    BSLSTL_MULTIMAP_REQUIRES_CONTAINER_COMPATIBLE_RANGE(RANGE, value_type)
    void insert_range(BSLS_COMPILERFEATURES_FORWARD_REF(RANGE) range)
    {
        // Defined inline to avoid Windows errors.

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)
        if constexpr (std::ranges::sized_range<RANGE>) {
            insertFromRange(bsl::ranges::begin(range),
                            bsl::ranges::end  (range),
                            bsl::ranges::size (range));
        } else // ...
#endif
        {
            insertFromRange(bsl::ranges::begin(range),
                            bsl::ranges::end  (range));
        }
    }

#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
    void insert(const_iterator first, const_iterator last);
        // This method is provided only on Sun to work around a bug in the Sun
        // Studio 12.3 compiler, which prevents us from disabling (at compile
        // time) the overload of 'insert' taking a 'const_iterator' and a
        // forwarding reference if the second argument is not convertible to
        // the value type associated with the map.  Without such a check, in
        // certain cases, the same compiler complains of ambiguity between
        // the 'insert' method taking two input iterators and the 'insert'
        // method taking a 'const_iterator' and a forwarding reference; such
        // an ambiguity is resolved by providing this method, which is
        // equivalent to the 'insert' method (above) taking two input iterators
        // of template parameter type.
#endif

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
    /// Insert into this multimap the value of each `value_type` object in
    /// the specified `values` initializer list.  This method requires that
    /// the (template parameter) types `KEY` and `VALUE` both be
    /// `copy-insertable` into this multimap (see {Requirements on `KEY` and
    /// `VALUE`}).
    void insert(std::initializer_list<value_type> values);
#endif

#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES // $var-args=2

    /// Insert into this multimap a newly-created `value_type` object,
    /// constructed by forwarding `get_allocator()` (if required) and the
    /// specified (variable number of) `args` to the corresponding
    /// constructor of `value_type`.  Return an iterator referring to the
    /// newly created and inserted object in this multimap.  This method
    /// requires that the (template parameter) types `KEY` and `VALUE` both
    /// be `emplace-constructible` from `args` (see {Requirements on `KEY`
    /// and `VALUE`}).
    template <class... Args>
    iterator emplace(Args&&... args);

    /// Insert into this multimap a newly-created `value_type` object,
    /// constructed by forwarding `get_allocator()` (if required) and the
    /// specified (variable number of) `args` to the corresponding
    /// constructor of `value_type` (in amortized constant time if the
    /// specified `hint` is a valid immediate successor to the `value_type`
    /// object constructed from `args`).  Return an iterator referring to
    /// the newly created and inserted object in this multimap.  If `hint`
    /// is not a valid immediate successor to the `value_type` object
    /// implied by `args`, this operation has `O[log(N)]` complexity where
    /// `N` is the size of this multimap.  This method requires that the
    /// (template parameter) types `KEY` and `VALUE` both be
    /// `emplace-constructible` from `args` (see {Requirements on `KEY` and
    /// `VALUE`}).  The behavior is undefined unless `hint` is an iterator
    /// in the range `[begin() .. end()]` (both endpoints included).
    template <class... Args>
    iterator emplace_hint(const_iterator hint, Args&&... args);
#endif

    /// Remove from this multimap the `value_type` object at the specified
    /// `position`, and return an iterator referring to the element
    /// immediately following the removed element, or to the past-the-end
    /// position if the removed element was the last element in the sequence
    /// of elements maintained by this multimap.   This method invalidates
    /// only iterators and references to the removed element and previously
    /// saved values of the `end()` iterator.  The behavior is undefined
    /// unless `position` refers to a `value_type` object in this multimap.
    iterator erase(const_iterator position);
    iterator erase(iterator position);

    /// Remove from this multimap all `value_type` objects whose keys are
    /// equivalent to the specified `key`, if such entries exist, and return
    /// the number of erased objects; otherwise, if there is no `value_type`
    /// objects having an equivalent key, return 0 with no other effect.
    /// This method invalidates only iterators and references to the removed
    /// element and previously saved values of the `end()` iterator.
    size_type erase(const key_type& key);
    template <class t_KEY>
    typename enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   t_KEY>::value &&
        !is_convertible<BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY),
                        iterator>::value &&
        !is_convertible<BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY),
                        const_iterator>::value,
    size_type>::type erase(BSLS_COMPILERFEATURES_FORWARD_REF(t_KEY) key)
    {
        // Implemented inline due to Sun CC compilation error.
        size_type count = 0;
        iterator  it    = this->lower_bound(key);
        while (it != end() && !key_comp()(key, it->first)) {
                           // !(it->first > key)
            it = erase(it);
            count++;
        }
        return count;
    }

    /// Remove from this multimap the `value_type` objects starting at the
    /// specified `first` position up to, but including the specified `last`
    /// position, and return `last`.   This method invalidates only
    /// iterators and references to the removed element and previously saved
    /// values of the `end()` iterator.  The behavior is undefined unless
    /// `first` and `last` either refer to elements in this multimap or are
    /// the `end` iterator, and the `first` position is at or before the
    /// `last` position in the ordered sequence provided by this container.
    iterator erase(const_iterator first, const_iterator last);

    void swap(multimap& other) BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                 AllocatorTraits::is_always_equal::value &&
                                 bsl::is_nothrow_swappable<COMPARATOR>::value);
        // Exchange the value and comparator of this object with those of the
        // specified 'other' object; also exchange the allocator of this object
        // with that of 'other' if the (template parameter) type 'ALLOCATOR'
        // has the 'propagate_on_container_swap' trait, and do not modify
        // either allocator otherwise.  This method provides the no-throw
        // exception-safety guarantee if and only if the (template parameter)
        // type 'COMPARATOR' provides a no-throw swap operation, and provides
        // the basic exception-safety guarantee otherwise; if an exception is
        // thrown, both objects are left in valid but unspecified states.  This
        // operation has 'O[1]' complexity if either this object was created
        // with the same allocator as 'other' or 'ALLOCATOR' has the
        // 'propagate_on_container_swap' trait; otherwise, it has 'O[n + m]'
        // complexity, where 'n' and 'm' are the number of elements in this
        // object and 'other', respectively.  Note that this method's support
        // for swapping objects created with different allocators when
        // 'ALLOCATOR' does not have the 'propagate_on_container_swap' trait is
        // a departure from the C++ Standard.

    /// Remove all entries from this multimap.  Note that the multimap is
    /// empty after this call, but allocated memory may be retained for
    /// future use.
    void clear() BSLS_KEYWORD_NOEXCEPT;

    // Turn off complaints about necessarily class-defined methods.
    // BDE_VERIFY pragma: push
    // BDE_VERIFY pragma: -CD01

    /// Return an iterator providing modifiable access to the first
    /// `value_type` object in this multimap whose key is equivalent to the
    /// specified `key`, if such an entry exists, and the past-the-end
    /// (`end`) iterator otherwise.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    iterator find(const key_type& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::find(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing modifiable access to the first
    /// `value_type` object in this multimap whose key is equivalent to the
    /// specified `key`, if such an entry exists, and the past-the-end
    /// (`end`) iterator otherwise.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        iterator>::type
    find(const LOOKUP_KEY& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::find(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing modifiable access to the first (i.e.,
    /// ordered least) `value_type` object in this multimap whose key is
    /// greater-than or equal-to the specified `key`, and the past-the-end
    /// iterator if this multimap does not contain a `value_type` object
    /// whose key is greater-than or equal-to `key`.  Note that this
    /// function returns the *first* position before which a `value_type`
    /// object having an equivalent key could be inserted into the ordered
    /// sequence maintained by this multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    iterator lower_bound(const key_type& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::lowerBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing modifiable access to the first (i.e.,
    /// ordered least) `value_type` object in this multimap whose key is
    /// greater-than or equal-to the specified `key`, and the past-the-end
    /// iterator if this multimap does not contain a `value_type` object
    /// whose key is greater-than or equal-to `key`.  Note that this
    /// function returns the *first* position before which a `value_type`
    /// object having an equivalent key could be inserted into the ordered
    /// sequence maintained by this multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        iterator>::type
    lower_bound(const LOOKUP_KEY& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::lowerBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing modifiable access to the first (i.e.,
    /// ordered least) `value_type` object in this multimap whose key is
    /// greater than the specified `key`, and the past-the-end iterator if
    /// this multimap does not contain a `value_type` object whose key is
    /// greater-than `key`.  Note that this function returns the *last*
    /// position before which a `value_type` object having an equivalent key
    /// could be inserted into the ordered sequence maintained by this
    /// multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    iterator upper_bound(const key_type& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::upperBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing modifiable access to the first (i.e.,
    /// ordered least) `value_type` object in this multimap whose key is
    /// greater than the specified `key`, and the past-the-end iterator if
    /// this multimap does not contain a `value_type` object whose key is
    /// greater-than `key`.  Note that this function returns the *last*
    /// position before which a `value_type` object having an equivalent key
    /// could be inserted into the ordered sequence maintained by this
    /// multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        iterator>::type
    upper_bound(const LOOKUP_KEY& key)
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::upperBound(
            d_tree, this->comparator(), key));
    }

    /// Return a pair of iterators providing modifiable access to the
    /// sequence of `value_type` objects in this multimap whose keys are
    /// equivalent to the specified `key`, where the first iterator is
    /// positioned at the start of the sequence and the second is positioned
    /// one past the end of the sequence.  The first returned iterator will
    /// be `lower_bound(key)`, the second returned iterator will be
    /// `upper_bound(key)`, and, if this multimap contains no `value_type`
    /// object with an equivalent key, then the two returned iterators will
    /// have the same value.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    bsl::pair<iterator,iterator> equal_range(const key_type& key)
    {
        iterator startIt = lower_bound(key);
        iterator endIt   = startIt;
        if (endIt != end() && !comparator()(key, *endIt.node())) {
            endIt = upper_bound(key);
        }
        return bsl::pair<iterator, iterator>(startIt, endIt);
    }

    /// Return a pair of iterators providing modifiable access to the
    /// sequence of `value_type` objects in this multimap whose keys are
    /// equivalent to the specified `key`, where the first iterator is
    /// positioned at the start of the sequence and the second is positioned
    /// one past the end of the sequence.  The first returned iterator will
    /// be `lower_bound(key)`, the second returned iterator will be
    /// `upper_bound(key)`, and, if this multimap contains no `value_type`
    /// object with an equivalent key, then the two returned iterators will
    /// have the same value.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        pair<iterator, iterator> >::type
    equal_range(const LOOKUP_KEY& key)
    {
        iterator startIt = lower_bound(key);
        iterator endIt   = startIt;
        if (endIt != end() && !comparator()(key, *endIt.node())) {
            endIt = upper_bound(key);
        }
        return pair<iterator, iterator>(startIt, endIt);
    }

    // BDE_VERIFY pragma: pop

    // ACCESSORS

    /// Return (a copy of) the allocator used for memory allocation by this
    /// multimap.
    allocator_type get_allocator() const BSLS_KEYWORD_NOEXCEPT;

    /// Return an iterator providing non-modifiable access to the first
    /// `value_type` object in the ordered sequence of `value_type` objects
    /// maintained by this multimap, or the `end` iterator if this multimap
    /// is empty.
    const_iterator begin() const BSLS_KEYWORD_NOEXCEPT;

    /// Return an iterator providing non-modifiable access to the
    /// past-the-end element in the ordered sequence of `value_type` objects
    /// maintained by this multimap.
    const_iterator end() const BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing non-modifiable access to the
    /// last `value_type` object in the ordered sequence of `value_type`
    /// objects maintained by this multimap, or `rend` if this multimap is
    /// empty.
    const_reverse_iterator rbegin() const BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing non-modifiable access to the
    /// prior-to-the-beginning element in the ordered sequence of
    /// `value_type` objects maintained by this multimap.
    const_reverse_iterator rend() const BSLS_KEYWORD_NOEXCEPT;

    /// Return an iterator providing non-modifiable access to the first
    /// `value_type` object in the ordered sequence of `value_type` objects
    /// maintained by this multimap, or the `cend` iterator if this multimap
    /// is empty.
    const_iterator cbegin() const BSLS_KEYWORD_NOEXCEPT;

    /// Return an iterator providing non-modifiable access to the
    /// past-the-end element in the ordered sequence of `value_type` objects
    /// maintained by this multimap.
    const_iterator cend() const BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing non-modifiable access to the
    /// last `value_type` object in the ordered sequence of `value_type`
    /// objects maintained by this multimap, or `rend` if this multimap is
    /// empty.
    const_reverse_iterator crbegin() const BSLS_KEYWORD_NOEXCEPT;

    /// Return a reverse iterator providing non-modifiable access to the
    /// prior-to-the-beginning element in the ordered sequence of
    /// `value_type` objects maintained by this multimap.
    const_reverse_iterator crend() const BSLS_KEYWORD_NOEXCEPT;

    /// Return `true` if this multimap contains an element whose key is
    /// equivalent to the specified `key`.
    bool contains(const key_type &key) const;

    /// Return `true` if this multimap contains an element whose key is
    /// equivalent to the specified `key`.
    ///
    /// Note: implemented inline due to Sun CC compilation error
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        bool>::type
    contains(const LOOKUP_KEY& key) const
    {
        return find(key) != end();
    }

    /// Return `true` if this multimap contains no elements, and `false`
    /// otherwise.
    bool empty() const BSLS_KEYWORD_NOEXCEPT;

    /// Return the number of elements in this multimap.
    size_type size() const BSLS_KEYWORD_NOEXCEPT;

    /// Return a theoretical upper bound on the largest number of elements
    /// that this multimap could possibly hold.  Note that there is no
    /// guarantee that the multimap can successfully grow to the returned
    /// size, or even close to that size without running out of resources.
    size_type max_size() const BSLS_KEYWORD_NOEXCEPT;

    /// Return the key-comparison functor (or function pointer) used by this
    /// multimap; if a comparator was supplied at construction, return its
    /// value, otherwise return a default constructed `key_compare` object.
    /// Note that this comparator compares objects of type `KEY`, which is
    /// the key part of the `value_type` objects contained in this multimap.
    key_compare key_comp() const;

    /// Return a functor for comparing two `value_type` objects by comparing
    /// their respective keys using `key_comp()`.   Note that this
    /// comparator compares objects of type `value_type` (i.e., 'pair<const
    /// KEY, VALUE>').
    value_compare value_comp() const;

    // Turn off complaints about necessarily class-defined methods.
    // BDE_VERIFY pragma: push
    // BDE_VERIFY pragma: -CD01

    /// Return an iterator providing non-modifiable access to the first
    /// `value_type` object having the specified `key` in the ordered
    /// sequence maintained by this multimap, if such an object exists, and
    /// the past-the-end (`end`) iterator otherwise.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    const_iterator find(const key_type& key) const
    {
        return const_iterator(BloombergLP::bslalg::RbTreeUtil::find(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing non-modifiable access to the first
    /// `value_type` object having the specified `key` in the ordered
    /// sequence maintained by this multimap, if such an object exists, and
    /// the past-the-end (`end`) iterator otherwise.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        const_iterator>::type
    find(const LOOKUP_KEY& key) const
    {
        return const_iterator(BloombergLP::bslalg::RbTreeUtil::find(
            d_tree, this->comparator(), key));
    }

    /// Return the number of `value_type` objects within this multimap whose
    /// keys are equivalent to the specified `key`.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    size_type count(const key_type& key) const
    {
        int            count = 0;
        const_iterator it    = lower_bound(key);

        while (it != end() && !comparator()(key, *it.node())) {
            ++it;
            ++count;
        }
        return count;
    }

    /// Return the number of `value_type` objects within this multimap whose
    /// keys are equivalent to the specified `key`.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        size_type>::type
    count(const LOOKUP_KEY& key) const
    {
        int            count = 0;
        const_iterator it    = lower_bound(key);

        while (it != end() && !comparator()(key, *it.node())) {
            ++it;
            ++count;
        }
        return count;
    }

    /// Return an iterator providing non-modifiable access to the first
    /// (i.e., ordered least) `value_type` object in this multimap whose key
    /// is greater-than or equal-to the specified `key`, and the
    /// past-the-end iterator if this multimap does not contain a
    /// `value_type` object whose key is greater-than or equal-to `key`.
    /// Note that this function returns the *first* position before which a
    /// `value_type` object having an equivalent key could be inserted into
    /// the ordered sequence maintained by this multimap, while preserving
    /// its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    const_iterator lower_bound(const key_type& key) const
    {
        return iterator(BloombergLP::bslalg::RbTreeUtil::lowerBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing non-modifiable access to the first
    /// (i.e., ordered least) `value_type` object in this multimap whose key
    /// is greater-than or equal-to the specified `key`, and the
    /// past-the-end iterator if this multimap does not contain a
    /// `value_type` object whose key is greater-than or equal-to `key`.
    /// Note that this function returns the *first* position before which a
    /// `value_type` object having an equivalent key could be inserted into
    /// the ordered sequence maintained by this multimap, while preserving
    /// its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        const_iterator>::type
    lower_bound(const LOOKUP_KEY& key) const
    {
        return const_iterator(BloombergLP::bslalg::RbTreeUtil::lowerBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing non-modifiable access to the first
    /// (i.e., ordered least) `value_type` object in this multimap whose key
    /// is greater than the specified `key`, and the past-the-end iterator
    /// if this multimap does not contain a `value_type` object whose key is
    /// greater-than `key`.  Note that this function returns the *last*
    /// position before which a `value_type` object having an equivalent key
    /// could be inserted into the ordered sequence maintained by this
    /// multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    const_iterator upper_bound(const key_type& key) const
    {
        return const_iterator(BloombergLP::bslalg::RbTreeUtil::upperBound(
            d_tree, this->comparator(), key));
    }

    /// Return an iterator providing non-modifiable access to the first
    /// (i.e., ordered least) `value_type` object in this multimap whose key
    /// is greater than the specified `key`, and the past-the-end iterator
    /// if this multimap does not contain a `value_type` object whose key is
    /// greater-than `key`.  Note that this function returns the *last*
    /// position before which a `value_type` object having an equivalent key
    /// could be inserted into the ordered sequence maintained by this
    /// multimap, while preserving its ordering.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        const_iterator>::type
    upper_bound(const LOOKUP_KEY& key) const
    {
        return const_iterator(BloombergLP::bslalg::RbTreeUtil::upperBound(
            d_tree, this->comparator(), key));
    }

    /// Return a pair of iterators providing non-modifiable access to the
    /// sequence of `value_type` objects in this multimap whose keys are
    /// equivalent to the specified `key`, where the first iterator is
    /// positioned at the start of the sequence and the second iterator is
    /// positioned one past the end of the sequence.  The first returned
    /// iterator will be `lower_bound(key)`, the second returned iterator
    /// will be `upper_bound(key)`, and, if this multimap contains no
    /// `value_type` objects having keys equivalent to `key`, then the two
    /// returned iterators will have the same value.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    pair<const_iterator, const_iterator> equal_range(const key_type& key) const
    {
        const_iterator startIt = lower_bound(key);
        const_iterator endIt   = startIt;
        if (endIt != end() && !comparator()(key, *endIt.node())) {
            endIt = upper_bound(key);
        }
        return bsl::pair<const_iterator, const_iterator>(startIt, endIt);
    }

    /// Return a pair of iterators providing non-modifiable access to the
    /// sequence of `value_type` objects in this multimap whose keys are
    /// equivalent to the specified `key`, where the first iterator is
    /// positioned at the start of the sequence and the second iterator is
    /// positioned one past the end of the sequence.  The first returned
    /// iterator will be `lower_bound(key)`, the second returned iterator
    /// will be `upper_bound(key)`, and, if this multimap contains no
    /// `value_type` objects having keys equivalent to `key`, then the two
    /// returned iterators will have the same value.
    ///
    /// Note: implemented inline due to Sun CC compilation error.
    template <class LOOKUP_KEY>
    typename bsl::enable_if<
        BloombergLP::bslmf::IsTransparentPredicate<COMPARATOR,
                                                   LOOKUP_KEY>::value,
        pair<const_iterator, const_iterator> >::type
    equal_range(const LOOKUP_KEY& key) const
    {
        const_iterator startIt = lower_bound(key);
        const_iterator endIt   = startIt;
        if (endIt != end() && !comparator()(key, *endIt.node())) {
            endIt = upper_bound(key);
        }
        return pair<const_iterator, const_iterator>(startIt, endIt);
    }

    // BDE_VERIFY pragma: pop
};

#ifdef BSLS_COMPILERFEATURES_SUPPORT_CTAD
// CLASS TEMPLATE DEDUCTION GUIDES

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `multimap`.  Deduce the
/// template parameters `COMPARATOR` and `ALLOCATOR` from the other
/// parameters passed to the constructor.  This deduction guide does not
/// participate unless the supplied allocator meets the requirements of a
/// standard allocator.
template <
    class INPUT_ITERATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class COMPARATOR = std::less<KEY>,
    class ALLOCATOR = bsl::allocator<
             BloombergLP::bslstl::IteratorUtil::IterToAlloc_t<INPUT_ITERATOR>>,
    class = bsl::enable_if_t<!bsl::IsStdAllocator_v<COMPARATOR>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
multimap(INPUT_ITERATOR,
    INPUT_ITERATOR,
    COMPARATOR = COMPARATOR(),
    ALLOCATOR = ALLOCATOR())
-> multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `multimap`.  Deduce the
/// template parameter `COMPARATOR` from the other parameter passed to the
/// constructor.  This deduction guide does not participate unless the
/// supplied allocator is convertible to
/// `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class COMPARATOR,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
multimap(INPUT_ITERATOR, INPUT_ITERATOR, COMPARATOR, ALLOC *)
-> multimap<KEY, VALUE, COMPARATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `multimap`.  This
/// deduction guide does not participate unless the supplied allocator meets
/// the requirements of a standard allocator.
template <
    class INPUT_ITERATOR,
    class ALLOCATOR,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
multimap(INPUT_ITERATOR, INPUT_ITERATOR, ALLOCATOR)
-> multimap<KEY, VALUE, std::less<KEY>, ALLOCATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the iterators supplied to the constructor of `multimap`.  This
/// deduction guide does not participate unless the supplied allocator is
/// convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class INPUT_ITERATOR,
    class ALLOC,
    class KEY = BloombergLP::bslstl::IteratorUtil::IterKey_t<INPUT_ITERATOR>,
    class VALUE =
               BloombergLP::bslstl::IteratorUtil::IterMapped_t<INPUT_ITERATOR>,
    class DEFAULT_ALLOCATOR = bsl::allocator<pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
multimap(INPUT_ITERATOR, INPUT_ITERATOR, ALLOC *)
-> multimap<KEY, VALUE>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `multimap`.
/// Deduce the template parameters `COMPARATOR` and `ALLOCATOR` from the
/// other parameters passed to the constructor.  This deduction guide does
/// not participate unless the supplied allocator meets the requirements of
/// a standard allocator.
template <
    class KEY,
    class VALUE,
    class COMPARATOR = std::less<KEY>,
    class ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<!bsl::IsStdAllocator_v<COMPARATOR>>,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
multimap(std::initializer_list<pair<const KEY, VALUE>>,
         COMPARATOR = COMPARATOR(),
         ALLOCATOR = ALLOCATOR())
-> multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `multimap`.
/// Deduce the template parameter `COMPARATOR` from the other parameters
/// passed to the constructor.  This deduction guide does not participate
/// unless the supplied allocator is convertible to
/// `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class COMPARATOR,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
multimap(std::initializer_list<pair<const KEY, VALUE>>, COMPARATOR, ALLOC *)
-> multimap<KEY, VALUE, COMPARATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `multimap`.
/// Deduce the template parameter `ALLOCATOR` from the other parameter
/// passed to the constructor.  This deduction guide does not participate
/// unless the supplied allocator meets the requirements of a standard
/// allocator.
template <
    class KEY,
    class VALUE,
    class ALLOCATOR,
    class = bsl::enable_if_t<bsl::IsStdAllocator_v<ALLOCATOR>>
    >
multimap(std::initializer_list<pair<const KEY, VALUE>>, ALLOCATOR)
-> multimap<KEY, VALUE, std::less<KEY>, ALLOCATOR>;

/// Deduce the template parameters `KEY` and `VALUE` from the `value_type`
/// of the initializer_list supplied to the constructor of `multimap`.  This
/// deduction guide does not participate unless the supplied allocator is
/// convertible to `bsl::allocator<bsl::pair<const KEY, VALUE>>`.
template <
    class KEY,
    class VALUE,
    class ALLOC,
    class DEFAULT_ALLOCATOR = bsl::allocator<bsl::pair<const KEY, VALUE>>,
    class = bsl::enable_if_t<bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>>
    >
multimap(std::initializer_list<pair<const KEY, VALUE>>, ALLOC *)
-> multimap<KEY, VALUE>;
#endif

// FREE OPERATORS

/// Return `true` if the specified `lhs` and `rhs` objects have the same
/// value, and `false` otherwise.  Two `multimap` objects `lhs` and `rhs`
/// have the same value if they have the same number of key-value pairs, and
/// each element in the ordered sequence of key-value pairs of `lhs` has the
/// same value as the corresponding element in the ordered sequence of
/// key-value pairs of `rhs`.  This method requires that the (template
/// parameter) types `KEY` and `VALUE` both be `equality-comparable` (see
/// {Requirements on `KEY` and `VALUE`}).
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator==(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);

#ifndef BSLS_COMPILERFEATURES_SUPPORT_THREE_WAY_COMPARISON
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator!=(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);
    // Return 'true' if the specified 'lhs' and 'rhs' objects do not have the
    // same value, and 'false' otherwise.  Two 'multimap' objects 'lhs' and
    // 'rhs' do not have the same value if they do not have the same number of
    // key-value pairs, or some element in the ordered sequence of key-value
    // pairs of 'lhs' does not have the same value as the corresponding element
    // in the ordered sequence of key-value pairs of 'rhs'.  This method
    // requires that the (template parameter) types 'KEY' and 'VALUE' both be
    // 'equality-comparable' (see {Requirements on 'KEY' and 'VALUE'}).
#endif

#ifdef BSLALG_SYNTHTHREEWAYUTIL_AVAILABLE

/// Perform a lexicographic three-way comparison of the specified `lhs` and
/// the specified `rhs` maps by using the comparison operators of
/// `bsl::pair<const KEY, VALUE>` on each element; return the result of that
/// comparison.
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
BloombergLP::bslalg::SynthThreeWayUtil::Result<pair<const KEY, VALUE>>
operator<=>(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
            const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);

#else

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator<(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
               const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);
    // Return 'true' if the value of the specified 'lhs' multimap is
    // lexicographically less than that of the specified 'rhs' multimap, and
    // 'false' otherwise.  Given iterators 'i' and 'j' over the respective
    // sequences '[lhs.begin() .. lhs.end())' and '[rhs.begin() .. rhs.end())',
    // the value of multimap 'lhs' is lexicographically less than that of
    // multimap 'rhs' if 'true == *i < *j' for the first pair of corresponding
    // iterator positions where '*i < *j' and '*j < *i' are not both 'false'.
    // If no such corresponding iterator position exists, the value of 'lhs' is
    // lexicographically less than that of 'rhs' if 'lhs.size() < rhs.size()'.
    // This method requires that 'operator<', inducing a total order, be
    // defined for 'value_type'.

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator>(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
               const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);
    // Return 'true' if the value of the specified 'lhs' multimap is
    // lexicographically greater than that of the specified 'rhs' multimap, and
    // 'false' otherwise.  The value of multimap 'lhs' is lexicographically
    // greater than that of multimap 'rhs' if 'rhs' is lexicographically less
    // than 'lhs' (see 'operator<').  This method requires that 'operator<',
    // inducing a total order, be defined for 'value_type'.  Note that this
    // operator returns 'rhs < lhs'.

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator<=(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);
    // Return 'true' if the value of the specified 'lhs' multimap is
    // lexicographically less than or equal to that of the specified 'rhs'
    // multimap, and 'false' otherwise.  The value of multimap 'lhs' is
    // lexicographically less than or equal to that of multimap 'rhs' if 'rhs'
    // is not lexicographically less than 'lhs' (see 'operator<').  This method
    // requires that 'operator<', inducing a total order, be defined for
    // 'value_type'.  Note that this operator returns '!(rhs < lhs)'.

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
bool operator>=(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs);
    // Return 'true' if the value of the specified 'lhs' multimap is
    // lexicographically greater than or equal to that of the specified 'rhs'
    // multimap, and 'false' otherwise.  The value of multimap 'lhs' is
    // lexicographically greater than or equal to that of multimap 'rhs' if
    // 'lhs' is not lexicographically less than 'rhs' (see 'operator<').  This
    // method requires that 'operator<', inducing a total order, be defined for
    // 'value_type'.  Note that this operator returns '!(lhs < rhs)'.

#endif  // BSLALG_SYNTHTHREEWAYUTIL_AVAILABLE

// FREE FUNCTIONS

/// Erase all the elements in the specified multimap `m` that satisfy the
/// specified predicate `predicate`.  Return the number of elements erased.
template <class KEY,
          class VALUE,
          class COMPARATOR,
          class ALLOCATOR,
          class PREDICATE>
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size_type
erase_if(multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>&               m,
                                                          PREDICATE predicate);

/// Exchange the value and comparator of the specified `a` object with those
/// of the specified `b` object; also exchange the allocator of `a` with
/// that of `b` if the (template parameter) type `ALLOCATOR` has the
/// `propagate_on_container_swap` trait, and do not modify either allocator
/// otherwise.  This function provides the no-throw exception-safety
/// guarantee if and only if the (template parameter) type `COMPARATOR`
/// provides a no-throw swap operation, and provides the basic
/// exception-safety guarantee otherwise; if an exception is thrown, both
/// objects are left in valid but unspecified states.  This operation has
/// `O[1]` complexity if either `a` was created with the same allocator as
/// `b` or `ALLOCATOR` has the `propagate_on_container_swap` trait;
/// otherwise, it has `O[n + m]` complexity, where `n` and `m` are the
/// number of elements in `a` and `b`, respectively.  Note that this
/// function's support for swapping objects created with different
/// allocators when `ALLOCATOR` does not have the
/// `propagate_on_container_swap` trait is a departure from the C++
/// Standard.
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
void swap(multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& a,
          multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& b)
             BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(false);

// ============================================================================
//                      INLINE FUNCTION DEFINITIONS
// ============================================================================

                             // -----------------
                             // class DataWrapper
                             // -----------------

// CREATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::DataWrapper::DataWrapper(
                                              const COMPARATOR& comparator,
                                              const ALLOCATOR&  basicAllocator)
: ::bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::Comparator(comparator)
, d_pool(basicAllocator)
{
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::DataWrapper::DataWrapper(
                          BloombergLP::bslmf::MovableRef<DataWrapper> original)
: ::bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::Comparator(
                                    MoveUtil::access(original).keyComparator())
, d_pool(MoveUtil::move(MoveUtil::access(original).d_pool))
{
}

// MANIPULATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::NodeFactory&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::DataWrapper::nodeFactory()
{
    return d_pool;
}

// ACCESSORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
const typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::NodeFactory&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::DataWrapper::nodeFactory() const
{
    return d_pool;
}

                             // -----------------------------
                             // class multimap::value_compare
                             // -----------------------------

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::value_compare::value_compare(
                                                         COMPARATOR comparator)
: comp(comparator)
{
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::value_compare::operator()(
                                                     const value_type& x,
                                                     const value_type& y) const
{
    return comp(x.first, y.first);
}

                             // --------------
                             // class multimap
                             // --------------

// PRIVATE MANIPULATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::Comparator&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::comparator()
{
    return d_compAndAlloc;
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::NodeFactory&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::nodeFactory()
{
    return d_compAndAlloc.nodeFactory();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::quickSwapExchangeAllocators(
                                                               multimap& other)
{
    BloombergLP::bslalg::RbTreeUtil::swap(&d_tree, &other.d_tree);
    nodeFactory().swapExchangeAllocators(other.nodeFactory());

    // 'DataWrapper' contains a 'NodeFactory' object and inherits from
    // 'Comparator'.  If the empty-base-class optimization has been applied to
    // 'Comparator', then we must not call 'swap' on it because
    // 'sizeof(Comparator) > 0' and, therefore, we will incorrectly swap bytes
    // of the 'NodeFactory' members!

    if (sizeof(NodeFactory) != sizeof(DataWrapper)) {
        comparator().swap(other.comparator());
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::quickSwapRetainAllocators(
                                                               multimap& other)
{
    BloombergLP::bslalg::RbTreeUtil::swap(&d_tree, &other.d_tree);
    nodeFactory().swapRetainAllocators(other.nodeFactory());

    // See 'quickSwapExchangeAllocators' (above).

    if (sizeof(NodeFactory) != sizeof(DataWrapper)) {
        comparator().swap(other.comparator());
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::constructFromRange(
                                                          INPUT_ITERATOR first,
                                                          SENTINEL       last)
{
    if (first == last) {
        return;                                                       // RETURN
    }

    if BSLS_KEYWORD_CONSTEXPR_CPP17 (
        BloombergLP::bslstl::IteratorUtil::
                      canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()) {
        nodeFactory().reserveNodes(
               BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));
    }

    BloombergLP::bslalg::RbTreeUtilTreeProctor<NodeFactory> proctor(
                                                               &d_tree,
                                                               &nodeFactory());

    // The following loop guarantees amortized linear time to insert an ordered
    // sequence of values (as required by the standard).   If the values are
    // in sorted order, we are guaranteed the next node can be inserted as the
    // right child of the previous node, and can call 'insertAt' without
    // 'findInsertLocation'.

    insert(*first);
    BloombergLP::bslalg::RbTreeNode *prevNode = d_tree.rootNode();

    while (++first != last) {

        const value_type& value = *first;
        if (this->comparator()(value.first, *prevNode)) {
            // The values are not in order, so insert them normally.
            insert(value);
            insertFromRange(++first, last);
            break;
        }

        // For multimap, we always insert even if keys are equal
        BloombergLP::bslalg::RbTreeNode *node =
                               nodeFactory().emplaceIntoNewNode(value);
        BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                                  prevNode,
                                                  false,
                                                  node);
        prevNode = node;
    }

    proctor.release();
}

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::constructFromRange(
                                                    INPUT_ITERATOR first,
                                                    SENTINEL       last,
                                                    size_t         numElements)

{
    BSLS_ASSERT_SAFE((
        !BloombergLP::bslstl::IteratorUtil
                       ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()
        || numElements == static_cast<size_type>(
             BloombergLP::bslstl::IteratorUtil::insertDistance(first, last))));

    if (first == last) {
        return;                                                       // RETURN
    }

    if (0 < numElements) {
        nodeFactory().reserveNodes(numElements);
    }

    BloombergLP::bslalg::RbTreeUtilTreeProctor<NodeFactory> proctor(
                                                               &d_tree,
                                                               &nodeFactory());

    // The following loop guarantees amortized linear time to insert an ordered
    // sequence of values (as required by the standard).   If the values are
    // in sorted order, we are guaranteed the next node can be inserted as the
    // right child of the previous node, and can call 'insertAt' without
    // 'findInsertLocation'.

    insert(*first); --numElements;
    BloombergLP::bslalg::RbTreeNode *prevNode = d_tree.rootNode();

    while (++first != last) {

        const value_type& value = *first;
        if (this->comparator()(value.first, *prevNode)) {
            // The values are not in order, so insert them normally.
            insert(value); --numElements;
            insertFromRange(++first, last, numElements);
            break;
        }

        // For multimap, we always insert even if keys are equal
        BloombergLP::bslalg::RbTreeNode *node =
                               nodeFactory().emplaceIntoNewNode(value);
        BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                                  prevNode,
                                                  false,
                                                  node);
        prevNode = node;
        --numElements;
    }

    proctor.release();
}

#endif

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insertFromRange(
                                                          INPUT_ITERATOR first,
                                                          SENTINEL       last)
{
    ///Implementation Notes
    ///--------------------
    // First, consume currently held free nodes.  Free nodes may be available
    // from previous insertions or from nodes reserved in `constructFromRange`.
    //
    // If those nodes are insufficient *and* one can calculate the remaining
    // number of elements, then reserve exactly that many free nodes.  There is
    // no more than one call to 'reserveNodes' per invocation of this method,
    // hence the use of 'BSLS_PERFORMANCEHINT_PREDICT_UNLIKELY'.

    while (first != last) {

        if (BloombergLP::bslstl::IteratorUtil
                       ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()
        && BSLS_PERFORMANCEHINT_PREDICT_UNLIKELY(
                                              !nodeFactory().hasFreeNodes())) {
            nodeFactory().reserveNodes(
               BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));
        }

        insert(*first);
        ++first;
    }
}

#if defined(BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS) \
 && defined(BSLS_LIBRARYFEATURES_HAS_CPP20_RANGES)

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR, class SENTINEL>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insertFromRange(
                                                    INPUT_ITERATOR first,
                                                    SENTINEL       last,
                                                    size_t         numElements)
{
    BSLS_ASSERT_SAFE((
        !BloombergLP::bslstl::IteratorUtil
                       ::canCalculateInsertDistance<INPUT_ITERATOR, SENTINEL>()
        || numElements == static_cast<size_type>(
             BloombergLP::bslstl::IteratorUtil::insertDistance(first, last))));

    while (first != last) {

        if (BSLS_PERFORMANCEHINT_PREDICT_UNLIKELY(
                                              !nodeFactory().hasFreeNodes())) {
            nodeFactory().reserveNodes(numElements);
        }

        insert(*first);
        --numElements;
        ++first;
    }
}

#endif

// PRIVATE ACCESSORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
const typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::Comparator&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::comparator() const
{
    return d_compAndAlloc;
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
const typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::NodeFactory&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::nodeFactory() const
{
    return d_compAndAlloc.nodeFactory();
}

// CREATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap()
: d_compAndAlloc(COMPARATOR(), ALLOCATOR())
, d_tree()
{
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                                               const ALLOCATOR& basicAllocator)
: d_compAndAlloc(COMPARATOR(), basicAllocator)
, d_tree()
{
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(const multimap& original)
: d_compAndAlloc(original.comparator().keyComparator(),
                 AllocatorTraits::select_on_container_copy_construction(
                                           original.nodeFactory().allocator()))
, d_tree()
{
    if (0 < original.size()) {
        nodeFactory().reserveNodes(original.size());
        BloombergLP::bslalg::RbTreeUtil::copyTree(&d_tree,
                                                  original.d_tree,
                                                  &nodeFactory());
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                             BloombergLP::bslmf::MovableRef<multimap> original)
: d_compAndAlloc(MoveUtil::move(MoveUtil::access(original).d_compAndAlloc))
, d_tree()
{
    multimap& lvalue = original;
    BloombergLP::bslalg::RbTreeUtil::swap(&d_tree, &lvalue.d_tree);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                 const multimap&                                original,
                 const typename type_identity<ALLOCATOR>::type& basicAllocator)
: d_compAndAlloc(original.comparator().keyComparator(), basicAllocator)
, d_tree()
{
    if (0 < original.size()) {
        nodeFactory().reserveNodes(original.size());
        BloombergLP::bslalg::RbTreeUtil::copyTree(&d_tree,
                                                  original.d_tree,
                                                  &nodeFactory());
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                 BloombergLP::bslmf::MovableRef<multimap> original,
                 const typename type_identity<ALLOCATOR>::type& basicAllocator)
: d_compAndAlloc(MoveUtil::access(original).comparator().keyComparator(),
                 basicAllocator)
, d_tree()
{
    multimap& lvalue = original;

    if (BSLS_PERFORMANCEHINT_PREDICT_LIKELY(
              nodeFactory().allocator() == lvalue.nodeFactory().allocator())) {
        d_compAndAlloc.nodeFactory().adopt(
                          MoveUtil::move(lvalue.d_compAndAlloc.nodeFactory()));
        BloombergLP::bslalg::RbTreeUtil::swap(&d_tree, &lvalue.d_tree);
    }
    else {
        if (0 < lvalue.size()) {
            nodeFactory().reserveNodes(lvalue.size());
            BloombergLP::bslalg::RbTreeUtil::moveTree(&d_tree,
                                                      &lvalue.d_tree,
                                                      &nodeFactory(),
                                                      &lvalue.nodeFactory());
        }
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                                              INPUT_ITERATOR    first,
                                              INPUT_ITERATOR    last,
                                              const COMPARATOR& comparator,
                                              const ALLOCATOR&  basicAllocator)
: d_compAndAlloc(comparator, basicAllocator)
, d_tree()
{
    if (first != last) {

        const size_type numElements = static_cast<size_type>(
            BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));

        if (0 < numElements) {
            nodeFactory().reserveNodes(numElements);
        }

        BloombergLP::bslalg::RbTreeUtilTreeProctor<NodeFactory> proctor(
                                                               &d_tree,
                                                               &nodeFactory());

        // The following loop guarantees amortized linear time to insert an
        // ordered sequence of values (as required by the standard).   If the
        // values are in sorted order, we are guaranteed the next node can be
        // inserted as the right child of the previous node, and can call
        // 'insertAt'.

        insert(*first);
        BloombergLP::bslalg::RbTreeNode *prevNode = d_tree.rootNode();
        while (++first != last) {
            // The values are not in order, so insert them normally.

            const value_type& value = *first;
            if (this->comparator()(value.first, *prevNode)) {
                insert(value);
                insert(++first, last);
                break;
            }
            BloombergLP::bslalg::RbTreeNode *node =
                nodeFactory().emplaceIntoNewNode(value);
            BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                                      prevNode,
                                                      false,
                                                      node);
            prevNode = node;
        }
        proctor.release();
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                                              INPUT_ITERATOR    first,
                                              INPUT_ITERATOR    last,
                                              const ALLOCATOR&  basicAllocator)
: d_compAndAlloc(COMPARATOR(), basicAllocator)
, d_tree()
{
    if (first != last) {

        const size_type numElements = static_cast<size_type>(
            BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));

        if (0 < numElements) {
            nodeFactory().reserveNodes(numElements);
        }

        BloombergLP::bslalg::RbTreeUtilTreeProctor<NodeFactory> proctor(
                                                               &d_tree,
                                                               &nodeFactory());

        // The following loop guarantees amortized linear time to insert an
        // ordered sequence of values (as required by the standard).   If the
        // values are in sorted order, we are guaranteed the next node can be
        // inserted as the right child of the previous node, and can call
        // 'insertAt'.

        insert(*first);
        BloombergLP::bslalg::RbTreeNode *prevNode = d_tree.rootNode();
        while (++first != last) {
            // The values are not in order, so insert them normally.

            const value_type& value = *first;
            if (this->comparator()(value.first, *prevNode)) {
                insert(value);
                insert(++first, last);
                break;
            }
            BloombergLP::bslalg::RbTreeNode *node =
                nodeFactory().emplaceIntoNewNode(value);
            BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                                      prevNode,
                                                      false,
                                                      node);
            prevNode = node;
        }
        proctor.release();
    }
}

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                              std::initializer_list<value_type> values,
                              const COMPARATOR&                 comparator,
                              const ALLOCATOR&                  basicAllocator)
: multimap(values.begin(), values.end(), comparator, basicAllocator)
{
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::multimap(
                              std::initializer_list<value_type> values,
                              const ALLOCATOR&                  basicAllocator)
: multimap(values.begin(), values.end(), COMPARATOR(), basicAllocator)
{
}
#endif

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::~multimap()
{
    clear();
}

// MANIPULATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::operator=(const multimap& rhs)
{
    if (BSLS_PERFORMANCEHINT_PREDICT_LIKELY(this != &rhs)) {
        if (AllocatorTraits::propagate_on_container_copy_assignment::value) {
            multimap other(rhs, rhs.nodeFactory().allocator());
            quickSwapExchangeAllocators(other);
        }
        else {
            multimap other(rhs, nodeFactory().allocator());
            quickSwapRetainAllocators(other);
        }
    }
    return *this;
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::operator=(
                                  BloombergLP::bslmf::MovableRef<multimap> rhs)
    BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                            AllocatorTraits::is_always_equal::value &&
                            std::is_nothrow_move_assignable<COMPARATOR>::value)
{
    multimap& lvalue = rhs;

    if (BSLS_PERFORMANCEHINT_PREDICT_LIKELY(this != &lvalue)) {
        if (nodeFactory().allocator() == lvalue.nodeFactory().allocator()) {
            multimap other(MoveUtil::move(lvalue));
            quickSwapRetainAllocators(other);
        }
        else if (
              AllocatorTraits::propagate_on_container_move_assignment::value) {
            multimap other(MoveUtil::move(lvalue));
            quickSwapExchangeAllocators(other);
        }
        else {
            multimap other(MoveUtil::move(lvalue), nodeFactory().allocator());
            quickSwapRetainAllocators(other);
        }
    }
    return *this;
}

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>&
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::operator=(
                                      std::initializer_list<value_type> values)
{
    clear();
    insert(values.begin(), values.end());
    return *this;
}
#endif

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::begin() BSLS_KEYWORD_NOEXCEPT
{
    return iterator(d_tree.firstNode());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::end() BSLS_KEYWORD_NOEXCEPT
{
    return iterator(d_tree.sentinel());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::rbegin() BSLS_KEYWORD_NOEXCEPT
{
    return reverse_iterator(end());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::rend() BSLS_KEYWORD_NOEXCEPT
{
    return reverse_iterator(begin());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insert(const value_type& value)
{
    bool leftChild;

    BloombergLP::bslalg::RbTreeNode *insertLocation =
        BloombergLP::bslalg::RbTreeUtil::findInsertLocation(&leftChild,
                                                            &d_tree,
                                                            this->comparator(),
                                                            value.first);

    BloombergLP::bslalg::RbTreeNode *node =
        nodeFactory().emplaceIntoNewNode(value);

    BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                              insertLocation,
                                              leftChild,
                                              node);
    return iterator(node);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class INPUT_ITERATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insert(INPUT_ITERATOR first,
                                                         INPUT_ITERATOR last)
{
    ///Implementation Notes
    ///--------------------
    // First, consume currently held free nodes.  Tf those nodes are
    // insufficient *and* one can calculate the remaining number of elements,
    // then reserve exactly that many free nodes.  There is no more than one
    // call to 'reserveNodes' per invocation of this method, hence the use of
    // 'BSLS_PERFORMANCEHINT_PREDICT_UNLIKELY'.

    while (first != last) {
        if (BloombergLP::bslstl::IteratorUtil
                 ::canCalculateInsertDistance<INPUT_ITERATOR, INPUT_ITERATOR>()
        && BSLS_PERFORMANCEHINT_PREDICT_UNLIKELY(
                                              !nodeFactory().hasFreeNodes())) {
            const size_type numElements = static_cast<size_type>(
               BloombergLP::bslstl::IteratorUtil::insertDistance(first, last));

            nodeFactory().reserveNodes(numElements);
        }
        insert(*first);
        ++first;
    }
}

#if defined(BSLS_PLATFORM_CMP_SUN) && BSLS_PLATFORM_CMP_VERSION < 0x5130
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insert(const_iterator first,
                                                         const_iterator last)
{
    while (first != last) {
        insert(*first);
        ++first;
    }
}
#endif

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insert(const_iterator    hint,
                                                    const value_type& value)
{
    bool leftChild;

    BloombergLP::bslalg::RbTreeNode *hintNode =
                const_cast<BloombergLP::bslalg::RbTreeNode *>(hint.node());

    BloombergLP::bslalg::RbTreeNode *insertLocation =
        BloombergLP::bslalg::RbTreeUtil::findInsertLocation(&leftChild,
                                                            &d_tree,
                                                            this->comparator(),
                                                            value.first,
                                                            hintNode);

    BloombergLP::bslalg::RbTreeNode *node =
        nodeFactory().emplaceIntoNewNode(value);

    BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                              insertLocation,
                                              leftChild,
                                              node);
    return iterator(node);
}

#if defined(BSLS_COMPILERFEATURES_SUPPORT_GENERALIZED_INITIALIZERS)
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::insert(
                                      std::initializer_list<value_type> values)
{
    insert(values.begin(), values.end());
}
#endif

#if !BSLS_COMPILERFEATURES_SIMULATE_CPP11_FEATURES
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class... Args>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::emplace(Args&&... args)
{
    bool leftChild;

    BloombergLP::bslalg::RbTreeNode *node = nodeFactory().emplaceIntoNewNode(
        BSLS_COMPILERFEATURES_FORWARD(Args, args)...);

    BloombergLP::bslalg::RbTreeNode *insertLocation =
        BloombergLP::bslalg::RbTreeUtil::findInsertLocation(
                               &leftChild,
                               &d_tree,
                               this->comparator(),
                               static_cast<const Node *>(node)->value().first);

    BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                              insertLocation,
                                              leftChild,
                                              node);
    return iterator(node);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
template <class... Args>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::emplace_hint(const_iterator hint,
                                                          Args&&...      args)
{
    bool leftChild;

    BloombergLP::bslalg::RbTreeNode *node = nodeFactory().emplaceIntoNewNode(
        BSLS_COMPILERFEATURES_FORWARD(Args, args)...);

    BloombergLP::bslalg::RbTreeNode *hintNode =
                    const_cast<BloombergLP::bslalg::RbTreeNode *>(hint.node());

    BloombergLP::bslalg::RbTreeNode *insertLocation =
        BloombergLP::bslalg::RbTreeUtil::findInsertLocation(
                                &leftChild,
                                &d_tree,
                                this->comparator(),
                                static_cast<const Node *>(node)->value().first,
                                hintNode);

    BloombergLP::bslalg::RbTreeUtil::insertAt(&d_tree,
                                              insertLocation,
                                              leftChild,
                                              node);
    return iterator(node);
}

#endif

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::erase(const_iterator position)
{
    BSLS_ASSERT_SAFE(position != end());

    BloombergLP::bslalg::RbTreeNode *node =
                const_cast<BloombergLP::bslalg::RbTreeNode *>(position.node());
    BloombergLP::bslalg::RbTreeNode *result =
                                   BloombergLP::bslalg::RbTreeUtil::next(node);
    BloombergLP::bslalg::RbTreeUtil::remove(&d_tree, node);
    nodeFactory().deleteNode(node);
    return iterator(result);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::erase(iterator position)
{
    return erase(const_iterator(position));
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size_type
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::erase(const key_type& key)
{
    size_type      count = 0;
    const_iterator first = find(key);

    if (first != end()) {
        const_iterator last = upper_bound(key);
        while (first != last) {
            first = erase(first);
            ++count;
        }
    }
    return count;
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::erase(const_iterator first,
                                                   const_iterator last)
{
    while (first != last) {
        first = erase(first);
    }
    return iterator(last.node());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::swap(multimap& other)
    BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(
                                  AllocatorTraits::is_always_equal::value &&
                                  bsl::is_nothrow_swappable<COMPARATOR>::value)
{
    if (AllocatorTraits::propagate_on_container_swap::value) {
        quickSwapExchangeAllocators(other);
    }
    else {
        // C++11 behavior for member 'swap': undefined for unequal allocators.
        // BSLS_ASSERT(allocator() == other.allocator());

        if (BSLS_PERFORMANCEHINT_PREDICT_LIKELY(
               nodeFactory().allocator() == other.nodeFactory().allocator())) {
            quickSwapRetainAllocators(other);
        }
        else {
            BSLS_PERFORMANCEHINT_UNLIKELY_HINT;

            multimap toOtherCopy(MoveUtil::move(*this),
                                 other.nodeFactory().allocator());
            multimap toThisCopy( MoveUtil::move(other),
                                 nodeFactory().allocator());

            this->quickSwapRetainAllocators(toThisCopy);
            other.quickSwapRetainAllocators(toOtherCopy);
        }
    }
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::clear() BSLS_KEYWORD_NOEXCEPT
{
    BSLS_ASSERT_SAFE(d_tree.firstNode());

    if (d_tree.rootNode()) {
        BSLS_ASSERT_SAFE(0 < d_tree.numNodes());
        BSLS_ASSERT_SAFE(d_tree.firstNode() != d_tree.sentinel());

        BloombergLP::bslalg::RbTreeUtil::deleteTree(&d_tree, &nodeFactory());
    }
#if defined(BSLS_ASSERT_SAFE_IS_USED)
    else {
        BSLS_ASSERT_SAFE(0 == d_tree.numNodes());
        BSLS_ASSERT_SAFE(d_tree.firstNode() == d_tree.sentinel());
    }
#endif
}

// ACCESSORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::allocator_type
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::get_allocator() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return nodeFactory().allocator();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::begin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return cbegin();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::end() const BSLS_KEYWORD_NOEXCEPT
{
    return cend();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::rbegin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return crbegin();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::rend() const BSLS_KEYWORD_NOEXCEPT
{
    return crend();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::cbegin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator(d_tree.firstNode());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::cend() const BSLS_KEYWORD_NOEXCEPT
{
    return const_iterator(d_tree.sentinel());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::crbegin() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_reverse_iterator(end());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::const_reverse_iterator
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::crend() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return const_reverse_iterator(begin());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::contains(
                                                     const key_type& key) const
{
    return find(key) != end();
}

// capacity:
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::empty() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return 0 == d_tree.numNodes();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size_type
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size() const BSLS_KEYWORD_NOEXCEPT
{
    return d_tree.numNodes();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size_type
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::max_size() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return AllocatorTraits::max_size(get_allocator());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::key_compare
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::key_comp() const
{
    return comparator().keyComparator();
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
typename multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::value_compare
multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::value_comp() const
{
    return value_compare(key_comp());
}

}  // close namespace bsl

// FREE OPERATORS
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator==(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return BloombergLP::bslalg::RangeCompare::equal(lhs.begin(),
                                                    lhs.end(),
                                                    lhs.size(),
                                                    rhs.begin(),
                                                    rhs.end(),
                                                    rhs.size());
}

#ifndef BSLS_COMPILERFEATURES_SUPPORT_THREE_WAY_COMPARISON
template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator!=(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return !(lhs == rhs);
}
#endif

#ifdef BSLALG_SYNTHTHREEWAYUTIL_AVAILABLE

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
BloombergLP::bslalg::SynthThreeWayUtil::Result<bsl::pair<const KEY, VALUE>>
bsl::operator<=>(const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                 const multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return bsl::lexicographical_compare_three_way(
                              lhs.begin(),
                              lhs.end(),
                              rhs.begin(),
                              rhs.end(),
                              BloombergLP::bslalg::SynthThreeWayUtil::compare);
}

#else

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator<(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return 0 > BloombergLP::bslalg::RangeCompare::lexicographical(lhs.begin(),
                                                                  lhs.end(),
                                                                  lhs.size(),
                                                                  rhs.begin(),
                                                                  rhs.end(),
                                                                  rhs.size());
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator>(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return rhs < lhs;
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator<=(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return !(rhs < lhs);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
bool bsl::operator>=(
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& lhs,
                   const bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& rhs)
{
    return !(lhs < rhs);
}

#endif  // BSLALG_SYNTHTHREEWAYUTIL_AVAILABLE

// FREE FUNCTIONS
template <class KEY,
          class VALUE,
          class COMPARATOR,
          class ALLOCATOR,
          class PREDICATE>
inline
typename bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>::size_type
bsl::erase_if(bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>&      m,
                                                           PREDICATE predicate)
{
    return BloombergLP::bslstl::AlgorithmUtil::containerEraseIf(m, predicate);
}

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
inline
void bsl::swap(bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& a,
               bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR>& b)
                                     BSLS_KEYWORD_NOEXCEPT_SPECIFICATION(false)
{
    a.swap(b);
}

// ============================================================================
//                                TYPE TRAITS
// ============================================================================

// Type traits for STL *ordered* containers:
//: o An ordered container defines STL iterators.
//: o An ordered container uses 'bslma' allocators if the (template parameter)
//:   type 'ALLOCATOR' is convertible from 'bslma::Allocator *'.

namespace BloombergLP {

namespace bslalg {

template <class KEY, class VALUE, class COMPARATOR, class ALLOCATOR>
struct HasStlIterators<bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR> >
    : bsl::true_type
{
};

}  // close namespace bslalg

namespace bslma {

template <class KEY,   class VALUE, class COMPARATOR, class ALLOCATOR>
struct UsesBslmaAllocator<bsl::multimap<KEY, VALUE, COMPARATOR, ALLOCATOR> >
    : bsl::is_convertible<Allocator*, ALLOCATOR>
{};

}  // close namespace bslma

}  // close enterprise namespace

#endif // End C++11 code

#endif

// ----------------------------------------------------------------------------
// Copyright 2019 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
