// bslmf_issame.h                                                     -*-C++-*-
#ifndef INCLUDED_BSLMF_ISSAME
#define INCLUDED_BSLMF_ISSAME

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

//@PURPOSE: Provide a meta-function for testing if two types are the same.
//
//@CLASSES:
//  bsl::is_same: standard meta-function for testing if two types are the same
//  bsl::is_same_v: the result value of the standard meta-function
//  bslmf::IsSame: meta-function for testing if two types are the same
//
//@DESCRIPTION: This component defines two meta-functions, `bsl::is_same` and
// `BloombergLP::bslmf::IsSame` and a template variable `bsl::is_same_v`,
// that represents the result value of the `bsl::is_same` meta-function.  All
// these meta-functions may be used to query whether two types are the same.
// Two types are the same if they name the same type having the same
// cv-qualifications.
//
// `bsl::is_same` meets the requirements of the `is_same` template defined in
// the C++11 standard [meta.rel], while `bslmf::IsSame` was devised before
// `is_same` was standardized.
//
// The two meta-functions are functionally equivalent.  The major difference
// between them is that the result for `bsl::is_same` is indicated by the class
// member `value`, while the result for `bslmf::IsSame` is indicated by the
// class member `value`.
//
// Note that `bsl::is_same` should be preferred over `bslmf::IsSame`, and in
// general, should be used by new components.
//
// Also note that the template variable `is_same_v` is defined in the C++17
// standard as an inline variable.  If the current compiler supports the inline
// variable C++17 compiler feature, `bsl::is_same_v` is defined as an
// `inline constexpr bool` variable.  Otherwise, if the compiler supports the
// variable templates C++14 compiler feature, `bsl::is_same_v` is defined as a
// non-inline `constexpr bool` variable.  See
// `BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES` and
// `BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES` macros in
// bsls_compilerfeatures component for details.
//
///Usage
///-----
// In this section we show intended use of this component.
//
///Example 1: Determine Same Types
///- - - - - - - - - - - - - - - -
// Suppose that we have several pairs of types and want to assert whether
// the types in each pair are the same.
//
// First, we define several `typedef`s:
// ```
// typedef       int    INT1;
// typedef       double DOUBLE;
// typedef       short  SHORT;
// typedef const short  CONST_SHORT;
// typedef       int    INT2;
// typedef       int&   INT_REF;
// ```
// Now, we instantiate the `bsl::is_same` template for certain pairs of the
// `typedef`s and assert the `value` static data member of each instantiation:
// ```
// assert(true  == (bsl::is_same<INT1, INT2>::value));
// assert(false == (bsl::is_same<INT, DOUBLE>::value));
// ```
// Note that a `const`-qualified type is considered distinct from the
// non-`const` (but otherwise identical) type:
// ```
// assert(false == (bsl::is_same<SHORT, CONST_SHORT>::value));
// ```
// Similarly, a `t_TYPE` and a reference to `t_TYPE` (`t_TYPE&`) are distinct:
// ```
// assert(false == (bsl::is_same<INT, INT_REF>::value));
// ```
// Note that if the current compiler supports the variable templates C++14
// feature then we can re-write the snippet of code above using the
// `bsl::is_same_v` variable as follows:
// ```
// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
//   assert(false == (bsl::is_same_v<SHORT, CONST_SHORT>));
//   assert(false == (bsl::is_same_v<INT, INT_REF>));
// #endif
// ```

#include <bslscm_version.h>

#include <bslmf_integralconstant.h>

#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>

namespace bsl {

                            // ==============
                            // struct is_same
                            // ==============

/// This `struct` template provides a meta-function to determine whether the
/// (template parameter) `t_TYPE1` and the (template parameter) `t_TYPE2`
/// are the same.  This generic default template derives from
/// `bsl::false_type`.  A template specialization is provided (below) that
/// derives from `bsl::true_type`.
template <class t_TYPE1, class t_TYPE2>
struct is_same : false_type {
};

/// This partial specialization of `is_same` derives from `bsl::true_type`
/// for when the (template parameter) types are the same.
template <class t_TYPE>
struct is_same<t_TYPE, t_TYPE> : true_type {
};

#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
/// This template variable represents the result value of the `bsl::is_same`
/// meta-function.
template <class t_TYPE1, class t_TYPE2>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_same_v =
                                              is_same<t_TYPE1, t_TYPE2>::value;
#endif

}  // close namespace bsl

namespace BloombergLP {

namespace bslmf {

                            // =============
                            // struct IsSame
                            // =============

/// This `struct` template implements a meta-function to determine if the
/// (template parameter) `t_TYPE1` and the (template parameter) `t_TYPE2`
/// are the same.  This `struct` derives from `bsl::true_type` if `t_TYPE1`
/// and `t_TYPE2` are the same, and `bsl::false_type` otherwise.
///
/// Note that although this `struct` is functionally equivalent to
/// `bsl::is_same`, the use of `bsl::is_same` should be preferred.
template <class t_TYPE1, class t_TYPE2>
struct IsSame : bsl::is_same<t_TYPE1, t_TYPE2>::type {
};

}  // close package namespace
}  // close enterprise namespace

#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================

#ifdef bslmf_IsSame
#undef bslmf_IsSame
#endif
/// This alias is defined for backward compatibility.
#define bslmf_IsSame bslmf::IsSame
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY

#endif

// ----------------------------------------------------------------------------
// Copyright 2013 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 ----------------------------------
