bslh_hashoptional.h

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/// @file bslh_hashoptional.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslh_hashoptional.h                                                -*-C++-*-
#ifndef INCLUDED_BSLH_HASHOPTIONAL
#define INCLUDED_BSLH_HASHOPTIONAL
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslh_hashoptional bslh_hashoptional
/// @brief  Provide `hashAppend` for `std::optional`.
/// @addtogroup bsl
/// @{
/// @addtogroup bslh
/// @{
/// @addtogroup bslh_hashoptional
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslh_hashoptional-purpose"> Purpose</a>
/// * <a href="#bslh_hashoptional-description"> Description </a>
///   * <a href="#bslh_hashoptional-usage"> Usage </a>
///     * <a href="#bslh_hashoptional-example-1-hashing-an-optional-boolean-value"> Example 1:  Hashing an optional Boolean value </a>
///
/// # Purpose {#bslh_hashoptional-purpose}
/// Provide `hashAppend` for `std::optional`.
///
/// # Description {#bslh_hashoptional-description}
/// This component provides a free function template,
/// `bslh::hashAppend`, overloaded for the `std::optional` class template.
/// Including this function allows for `std::optional` types (and types that
/// contain them) to be used as keys in BDE hashed containers.
///
/// Note that use of this component requires that the language standard be 2017
/// or later, as that is when `std::optional` first appears.
///
/// ## Usage {#bslh_hashoptional-usage}
///
///
/// This section illustrates intended usage of this component.
///
/// ### Example 1:  Hashing an optional Boolean value {#bslh_hashoptional-example-1-hashing-an-optional-boolean-value}
///
///
/// Suppose we want to maintain a boolean condition as either true, false, or
/// unspecified, and have it fit within the BDE hash framework.  We can use
/// `std::optional<bool>` for this, and demonstrate that such a value can be
/// correctly hashed.
///
/// First, we set up three such optional values to represent the three possible
/// states we wish to represent.
/// @code
/// std::optional<bool> optionalTrue  = true;
/// std::optional<bool> optionalFalse = false;
/// std::optional<bool> optionalUnset;
/// @endcode
/// Then, we create a hashing object.
/// @code
/// bslh::Hash<> hasher;
/// @endcode
/// Next, we hash each of our values.
/// @code
/// size_t optionalTrueHash  = hasher(optionalTrue);
/// size_t optionalFalseHash = hasher(optionalFalse);
/// size_t optionalUnsetHash = hasher(optionalUnset);
/// @endcode
/// Then we hash the underlying values.
/// @code
/// size_t expectedTrueHash  = hasher(true);
/// size_t expectedFalseHash = hasher(false);
/// @endcode
/// Finally, we verify that the `std::optional` hasher produces the same results
/// as the underlying hashers.  For the disengaged hash, we will just check that
/// the value differs from either engaged value.
/// @code
/// assert(expectedTrueHash  == optionalTrueHash);
/// assert(expectedFalseHash == optionalFalseHash);
/// assert(expectedTrueHash  != optionalUnsetHash);
/// assert(expectedFalseHash != optionalUnsetHash);
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslh
 * @{
 */
/** @addtogroup bslh_hashoptional
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslh_hash.h>
 
#include <bslmf_removeconst.h>
 
#include <bsls_libraryfeatures.h>
#include <bsls_platform.h>
 
#include <stddef.h>  // for 'size_t'
#include <string.h>  // for 'strlen'
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY
 
#include <optional>
 
 
namespace bslh {
 
// FREE FUNCTIONS
 
/// If the specified `input` is engaged, pass its contained value into the
/// specified `algorithm` to be combined into the internal state of the
/// algorithm that is used to produce the resulting hash value.  Otherwise,
/// pass an arbitrary `size_t` value instead.  Note that this behavior (for
/// engaged values) is required by the C++ Standard.
template <class HASH_ALGORITHM, class TYPE>
inline
void
hashAppend(HASH_ALGORITHM& algorithm, const std::optional<TYPE> &input)
{
    if (input) {
        hashAppend(algorithm, input.value());
    } else {
        size_t disengaged = 0xB01DFACE;
        hashAppend(algorithm, disengaged);
    }
}
 
}  // close package namespace
 
 
#endif  // BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2020 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */