bslmf_islvaluereference.h

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/// @file bslmf_islvaluereference.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_islvaluereference.h                                          -*-C++-*-
#ifndef INCLUDED_BSLMF_ISLVALUEREFERENCE
#define INCLUDED_BSLMF_ISLVALUEREFERENCE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_islvaluereference bslmf_islvaluereference
/// @brief  Provide a compile-time check for lvalue reference types.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_islvaluereference
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_islvaluereference-purpose"> Purpose</a>
/// * <a href="#bslmf_islvaluereference-classes"> Classes </a>
/// * <a href="#bslmf_islvaluereference-description"> Description </a>
///   * <a href="#bslmf_islvaluereference-usage"> Usage </a>
///     * <a href="#bslmf_islvaluereference-example-1-verify-lvalue-reference-types"> Example 1: Verify Lvalue Reference Types </a>
///
/// # Purpose {#bslmf_islvaluereference-purpose}
/// Provide a compile-time check for lvalue reference types.
///
/// # Classes {#bslmf_islvaluereference-classes}
///
/// -  bsl::is_lvalue_reference: standard meta-function for lvalue reference types
/// -  bsl::is_lvalue_reference_v: the result value of the meta-function
///
/// @see  bslmf_integralconstant
///
/// # Description {#bslmf_islvaluereference-description}
/// This component defines a meta-function,
/// `bsl::is_lvalue_reference` and a template variable
/// `bsl::is_lvalue_reference_v`, that represents the result value of the
/// `bsl::is_lvalue_reference` meta-function, that may be used to query whether
/// a type is an lvalue reference type.
///
/// `bsl::is_lvalue_reference` meets the requirements of the
/// `is_lvalue_reference` template defined in the C++11 standard
/// [meta.unary.cat].
///
/// Note that the template variable `is_lvalue_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_lvalue_reference_v` is
/// defined as an `inline constexpr bool` variable.  Otherwise, if the compiler
/// supports the variable templates C++14 compiler feature,
/// `bsl::is_lvalue_reference_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_islvaluereference-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Verify Lvalue Reference Types {#bslmf_islvaluereference-example-1-verify-lvalue-reference-types}
///
///
/// Suppose that we want to assert whether a set of types are lvalue reference
/// types.
///
/// Now, we instantiate the `bsl::is_lvalue_reference` template for both a
/// non-reference type and an lvalue reference type, and assert the `value`
/// static data member of each instantiation:
/// @code
/// assert(false == bsl::is_lvalue_reference<int>::value);
/// assert(true  == bsl::is_lvalue_reference<int&>::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_lvalue_reference_v` variable as follows:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
///   assert(false == bsl::is_lvalue_reference_v<int>);
///   assert(true  == bsl::is_lvalue_reference_v<int&>);
/// #endif
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_islvaluereference
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
#include <bsls_libraryfeatures.h>
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_BASELINE_LIBRARY
#include <type_traits> // 'std::is_lvalue_reference' and
                       // 'std::is_lvalue_reference_v' (C++17)
#endif
 
namespace bsl {
                          // ==========================
                          // struct is_lvalue_reference
                          // ==========================
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_BASELINE_LIBRARY
template <class t_TYPE>
struct is_lvalue_reference : bsl::integral_constant<
                                       bool,
                                       std::is_lvalue_reference<t_TYPE>::value>
{};
 
#else
 
/// This `struct` template provides a meta-function to determine whether the
/// (template parameter) `t_TYPE` is a (possibly cv-qualified) lvalue
/// reference type.  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_lvalue_reference : false_type {
};
 
/// This partial specialization of `is_lvalue_reference` derives from
/// `bsl::true_type` for when the (template parameter) `t_TYPE` is an lvalue
/// reference type.
template <class t_TYPE>
struct is_lvalue_reference<t_TYPE&> : true_type {
};
#endif // BSLS_LIBRARYFEATURES_HAS_CPP11_BASELINE_LIBRARY
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY
using std::is_lvalue_reference_v;
#else
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
template <class t_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_lvalue_reference_v =
                                            is_lvalue_reference<t_TYPE>::value;
    // This template variable represents the result value of the
    // 'bsl::is_lvalue_reference' meta-function.
#endif
#endif // BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY
 
}  // 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */