bslmf_issame.h

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/// @file bslmf_issame.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_issame.h                                                     -*-C++-*-
#ifndef INCLUDED_BSLMF_ISSAME
#define INCLUDED_BSLMF_ISSAME
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_issame bslmf_issame
/// @brief  Provide a meta-function for testing if two types are the same.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_issame
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_issame-purpose"> Purpose</a>
/// * <a href="#bslmf_issame-classes"> Classes </a>
/// * <a href="#bslmf_issame-description"> Description </a>
///   * <a href="#bslmf_issame-usage"> Usage </a>
///     * <a href="#bslmf_issame-example-1-determine-same-types"> Example 1: Determine Same Types </a>
///
/// # Purpose {#bslmf_issame-purpose}
/// Provide a meta-function for testing if two types are the same.
///
/// # Classes {#bslmf_issame-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 {#bslmf_issame-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 {#bslmf_issame-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Determine Same Types {#bslmf_issame-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:
/// @code
/// typedef       int    INT1;
/// typedef       double DOUBLE;
/// typedef       short  SHORT;
/// typedef const short  CONST_SHORT;
/// typedef       int    INT2;
/// typedef       int&   INT_REF;
/// @endcode
/// 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:
/// @code
/// assert(true  == (bsl::is_same<INT1, INT2>::value));
/// assert(false == (bsl::is_same<INT, DOUBLE>::value));
/// @endcode
/// Note that a `const`-qualified type is considered distinct from the
/// non-`const` (but otherwise identical) type:
/// @code
/// assert(false == (bsl::is_same<SHORT, CONST_SHORT>::value));
/// @endcode
/// Similarly, a `t_TYPE` and a reference to `t_TYPE` (`t_TYPE&`) are distinct:
/// @code
/// assert(false == (bsl::is_same<INT, INT_REF>::value));
/// @endcode
/// 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:
/// @code
/// #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
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_issame
 * @{
 */
 
#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 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 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
 
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */