bslmf_isclass.h

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/// @file bslmf_isclass.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_isclass.h                                                    -*-C++-*-
#ifndef INCLUDED_BSLMF_ISCLASS
#define INCLUDED_BSLMF_ISCLASS
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_isclass bslmf_isclass
/// @brief  Provide a compile-time check for determining class types.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_isclass
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_isclass-purpose"> Purpose</a>
/// * <a href="#bslmf_isclass-classes"> Classes </a>
/// * <a href="#bslmf_isclass-description"> Description </a>
///   * <a href="#bslmf_isclass-usage"> Usage </a>
///     * <a href="#bslmf_isclass-example-1-verify-class-types"> Example 1: Verify Class Types </a>
///
/// # Purpose {#bslmf_isclass-purpose}
/// Provide a compile-time check for determining class types.
///
/// # Classes {#bslmf_isclass-classes}
///
/// -  bsl::is_class: standard meta-function for determining class types
/// -  bsl::is_class_v: the result value of the `bsl::is_class` meta-function
/// -  bslmf::IsClass: meta-function for determining class types
///
/// # Description {#bslmf_isclass-description}
/// This component defines two meta-functions, `bsl::is_class` and
/// `BloombergLP::bslmf::IsClass` and a template variable `bsl::is_class_v`,
/// that represents the result value of the `bsl::is_class` meta-function.  All
/// these meta-functions may be used to query whether a type is a `class`,
/// `struct`, or `union`, optionally qualified with `const` or `volatile`.
///
/// `bsl::is_class` meets the requirements of the `is_class` template defined in
/// the C++11 standard [meta.unary.cat], while `bslmf::IsClass` was devised
/// before `is_class` was standardized.
///
/// The two meta-functions are functionally equivalent.  The major difference
/// between them is that the result for `bsl::is_class` is indicated by the
/// class member `value`, while the result for `bslmf::IsClass` is indicated by
/// the class member `value`.
///
/// Note that `bsl::is_class` should be preferred over `bslmf::IsClass`, and in
/// general, should be used by new components.
///
/// Also note that the template variable `is_class_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_class_v` is defined as an
/// `inline constexpr bool` variable.  Otherwise, if the compiler supports the
/// variable templates C++14 compiler feature, `bsl::is_class_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_isclass-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Verify Class Types {#bslmf_isclass-example-1-verify-class-types}
///
///
/// Suppose that we want to assert whether a set of types are class types.
///
/// First, we create a class type `MyClass`:
/// @code
/// class MyClass
/// {
/// };
/// @endcode
/// Now, we instantiate the `bsl::is_class` template for both a non-class type
/// and the defined type `MyClass`, and assert the `value` static data member of
/// each instantiation:
/// @code
/// assert(false == bsl::is_class<int>::value);
/// assert(true  == bsl::is_class<MyClass>::value);
/// @endcode
/// Note that if the current compiler supports the variable the templates C++14
/// feature then we can re-write the snippet of code above using the
/// `bsl::is_class_v` variable as follows:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
///   assert(false == bsl::is_class_v<int>);
///   assert(true  == bsl::is_class_v<MyClass>);
/// #endif
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_isclass
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
#include <bslmf_voidtype.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bslmf_removecv.h>
#include <cstdlib>
#endif
 
 
namespace bslmf {
 
                             // ==================
                             // struct IsClass_Imp
                             // ==================
 
/// This `struct` template provides a meta-function to determine whether the
/// (template parameter) `t_TYPE` is a class type.
template <class t_TYPE, class = void>
struct IsClass_Imp : bsl::false_type {
};
 
/// This `struct` template provides a meta-function to determine whether the
/// (template parameter) `t_TYPE` is a class type.
template <class t_TYPE>
struct IsClass_Imp<t_TYPE, BSLMF_VOIDTYPE(int t_TYPE::*)> : bsl::true_type {
};
 
}  // close package namespace
 
 
namespace bsl {
 
                             // ===============
                             // struct is_class
                             // ===============
 
/// This `struct` template implements the `is_class` meta-function defined
/// in the C++11 standard [meta.unary.cat] to determine if the (template
/// parameter) `t_TYPE` is a class.  Note that for implementations without
/// native library support, this component will mis-diagnose `union` types
/// as classes.  This would be correct according to the core language
/// definition of a class type, but is an error according to the standard
/// library definition of this type trait.
template <class t_TYPE>
struct is_class : BloombergLP::bslmf::IsClass_Imp<t_TYPE>::type {
};
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
/// This template variable represents the result value of the
/// `bsl::is_class` meta-function.
template <class t_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_class_v =
                                                       is_class<t_TYPE>::value;
#endif
 
}  // close namespace bsl
 
 
namespace bslmf {
                            // ==============
                            // struct IsClass
                            // ==============
 
/// This meta-function derives from `bsl::true_type` if the (template
/// parameter) `t_TYPE` is a class type, or a reference to a class type, and
/// from `bsl::false_type` otherwise.
///
/// Note that although this `struct` is functionally identical to
/// `bsl::is_class`, the use of `bsl::is_class` should be preferred.
template <class t_TYPE>
struct IsClass : bsl::is_class<t_TYPE>::type {
};
 
}  // close package namespace
 
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
#ifdef bslmf_IsClass
#undef bslmf_IsClass
#endif
/// This alias is defined for backward compatibility.
#define bslmf_IsClass bslmf::IsClass
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2019 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */