// 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
// ==============
template <class t_TYPE1, class t_TYPE2>
struct is_same : false_type {
// 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_TYPE>
struct is_same<t_TYPE, t_TYPE> : true_type {
// This partial specialization of 'is_same' derives from 'bsl::true_type'
// for when the (template parameter) types are the same.
};
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
template <class t_TYPE1, class t_TYPE2>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_same_v =
is_same<t_TYPE1, t_TYPE2>::value;
// This template variable represents the result value of the 'bsl::is_same'
// meta-function.
#endif
} // close namespace bsl
namespace BloombergLP {
namespace bslmf {
// =============
// struct IsSame
// =============
template <class t_TYPE1, class t_TYPE2>
struct IsSame : bsl::is_same<t_TYPE1, t_TYPE2>::type {
// 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.
};
} // close package namespace
} // close enterprise namespace
#ifndef BDE_OPENSOURCE_PUBLICATION // BACKWARD_COMPATIBILITY
// ============================================================================
// BACKWARD COMPATIBILITY
// ============================================================================
#ifdef bslmf_IsSame
#undef bslmf_IsSame
#endif
#define bslmf_IsSame bslmf::IsSame
// This alias is defined for backward compatibility.
#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 ----------------------------------