// bslh_hashpair.h                                                    -*-C++-*-
#ifndef INCLUDED_BSLH_HASHPAIR
#define INCLUDED_BSLH_HASHPAIR

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

//@PURPOSE: Provide `hashAppend` for `std::pair`.
//
//@DESCRIPTION: This component provides a free function template,
// `bslh::hashAppend`, overloaded for the `std::pair` class template.
// Including this function allows for `std::pair` types (and types that contain
// them) to be used as keys in BDE hashed containers.
//
///Usage
///-----
// This section illustrates intended usage of this component.
//
///Example 1: Hashing a Pair of Integer Values
/// - - - - - - - - - - - - - - - - - - - - - -
// Suppose one must compute has that combines the hashes of several integer
// values, each of a different type:
// ```
// char  c = 'a';
// short s = static_cast<short>(1);
// ```
// First, we can make that calculation by repeated invocations of a
// 'bslh::DefaultHashAlogorithm object:
// ```
// bslh::DefaultHashAlgorithm hasherS;
// hasherS(&c, sizeof(char));
// hasherS(&s, sizeof(short));
//
// bslh::DefaultHashAlgorithm::result_type hashS = hasherS.computeHash();
// ```
// Now, the same calculation can also be be made if those same values are
// contained in a single `std::pair` object.
// ```
// std::pair<char, short> t = std::make_pair(c, s);
//
// bslh::DefaultHashAlgorithm hasherT;
// bslh::hashAppend(hasherT, t);
//
// bslh::DefaultHashAlgorithm::result_type hashT = hasherT.computeHash();
// ```
// Finally, we confirm that we computed the same result.
// ```
// assert(hashS == hashT);
// ```

#include <bslscm_version.h>

#include <bslh_hash.h>

#include <utility> // 'std::pair'

namespace BloombergLP {
namespace bslh {

// FREE FUNCTIONS

/// Invoke the (appropriate) `hashAppend` function, with the specified
/// `algorithm` on the `first` and `second` members, in that order, of the
/// specified `input` pair.
template <class HASH_ALGORITHM, class TYPE1, class TYPE2>
void
hashAppend(HASH_ALGORITHM& algorithm, const std::pair<TYPE1, TYPE2>& input);

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

// FREE FUNCTIONS
template <class HASH_ALGORITHM, class TYPE1, class TYPE2>
inline
void
hashAppend(HASH_ALGORITHM& algorithm, const std::pair<TYPE1, TYPE2>& input)
{
    hashAppend(algorithm, input.first);
    hashAppend(algorithm, input.second);
}

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

#endif

// ----------------------------------------------------------------------------
// Copyright 2021 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 ----------------------------------
