bslmf_isreference.h

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/// @file bslmf_isreference.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_isreference.h                                                -*-C++-*-
#ifndef INCLUDED_BSLMF_ISREFERENCE
#define INCLUDED_BSLMF_ISREFERENCE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_isreference bslmf_isreference
/// @brief  Provide a meta-function to test reference types.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_isreference
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_isreference-purpose"> Purpose</a>
/// * <a href="#bslmf_isreference-classes"> Classes </a>
/// * <a href="#bslmf_isreference-description"> Description </a>
///   * <a href="#bslmf_isreference-usage"> Usage </a>
///     * <a href="#bslmf_isreference-example-1-verify-reference-types"> Example 1: Verify Reference Types </a>
///
/// # Purpose {#bslmf_isreference-purpose}
/// Provide a meta-function to test reference types.
///
/// # Classes {#bslmf_isreference-classes}
///
/// -  bsl::is_reference: standard meta-function for testing reference types
/// -  bsl::is_reference_v: the result value of the standard meta-function
///
/// @see 
///
/// # Description {#bslmf_isreference-description}
/// This component defines a meta-function, `bsl::is_reference` and
/// a template variable `bsl::is_reference_v`, that represents the result value
/// of the `bsl::is_class` meta-function, that may be used to query whether a
/// type is an (lvalue or rvalue) reference type.
///
/// `bsl::is_reference` meets the requirements of the `is_reference` template
/// defined in the C++11 standard [meta.unary.comp].
///
/// Note that the template variable `is_reference_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_reference_v` is defined as an
/// `inline constexpr bool` variable.  Otherwise, if the compiler supports the
/// variable templates C++14 compiler feature, `bsl::is_reference_v` is defined
/// as a non-`const` `constexpr bool` variable.  See
/// `BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES` and
/// `BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES` macros in
/// bsls_compilerfeatures component for details.
///
/// ## Usage {#bslmf_isreference-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Verify Reference Types {#bslmf_isreference-example-1-verify-reference-types}
///
///
/// Suppose that we want to assert whether a set of types are (lvalue or rvalue)
/// reference types.
///
/// Now, we instantiate the `bsl::is_reference` template for a non-reference
/// type, an lvalue reference type, and an rvalue reference type, and assert the
/// `value` static data member of each instantiation:
/// @code
/// assert(false == bsl::is_reference<int>::value);
/// assert(true  == bsl::is_reference<int&>::value);
/// #if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES)
/// assert(true  == bsl::is_reference<int&&>::value);
/// #endif
/// @endcode
/// Note that rvalue reference is a feature introduced in the C++11 standand,
/// and may not be supported by all compilers.
///
/// Also 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_reference_v` variable as follows:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
///   assert(false == bsl::is_reference_v<int>);
///   assert(true  == bsl::is_reference_v<int&>);
///   assert(true  == bsl::is_reference_v<int&&>);
/// #endif
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_isreference
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bslmf_islvaluereference.h>
#include <bslmf_isrvaluereference.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
 
namespace bsl {
 
                         // ===================
                         // struct is_reference
                         // ===================
 
// IMPLEMENTATION NOTE:  We originally implemented this trait in terms of
// 'is_lvalue_reference' and 'is_rvalue_reference' but ran into an issue on
// Sun where the compiler was reporting that the maximum depth of template
// expansion was being exceeded.
 
/// This `struct` template implements the `is_reference` meta-function
/// defined in the C++11 standard [meta.unary.comp] to determine if the
/// (template parameter) `t_TYPE` is a (lvalue or rvalue) reference type.
///
/// This `struct` derives from `bsl::false_type` with specializations to
/// follow for lvalue and rvalue references.
template <class t_TYPE>
struct is_reference : false_type {
};
 
/// This `struct` template implements the `is_reference` meta-function
/// defined in the C++11 standard [meta.unary.comp] to determine if the
/// (template parameter) `t_TYPE` is a (lvalue or rvalue) reference type.
///
/// This specialization for lvalue references derives from `bsl::true_type`.
template <class t_TYPE>
struct is_reference<t_TYPE&> : true_type {
};
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES)
/// This `struct` template implements the `is_reference` meta-function
/// defined in the C++11 standard [meta.unary.comp] to determine if the
/// (template parameter) `t_TYPE` is a (lvalue or rvalue) reference type.
///
/// This specialization for rvalue references derives from 'bsl::true_type.
template <class t_TYPE>
struct is_reference<t_TYPE&&> : true_type {
};
#endif
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
/// This template variable represents the result value of the
/// `bsl::is_reference` meta-function.
template <class t_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_reference_v =
                                                   is_reference<t_TYPE>::value;
#endif
 
}  // close namespace bsl
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */