bslmf_isvoid.h

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/// @file bslmf_isvoid.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_isvoid.h                                                     -*-C++-*-
#ifndef INCLUDED_BSLMF_ISVOID
#define INCLUDED_BSLMF_ISVOID
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_isvoid bslmf_isvoid
/// @brief  Provide a compile-time check for `void` types.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_isvoid
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_isvoid-purpose"> Purpose</a>
/// * <a href="#bslmf_isvoid-classes"> Classes </a>
/// * <a href="#bslmf_isvoid-description"> Description </a>
///   * <a href="#bslmf_isvoid-usage"> Usage </a>
///     * <a href="#bslmf_isvoid-example-1-determine-whether-a-type-is-the-void-type"> Example 1: Determine Whether a Type is the void Type </a>
///
/// # Purpose {#bslmf_isvoid-purpose}
/// Provide a compile-time check for `void` types.
///
/// # Classes {#bslmf_isvoid-classes}
///
/// -  bsl::is_void: standard meta-function for determining `void` types
/// -  bsl::is_void_v: the result value of the `bsl::is_void` meta-function
/// -  bslmf::IsVoid: meta-function for determining `void` types
///
/// @see  bslmf_integralconstant
///
/// # Description {#bslmf_isvoid-description}
/// This component defines two meta-functions, `bsl::is_void` and
/// `BloombergLP::bslmf::IsVoid` and a template variable `bsl::is_void_v`, that
/// represents the result value of `bsl::is_void` meta-function.  All these
/// meta-functions may be used to query whether a type is the (possibly
/// cv-qualified) `void` type.
///
/// `bsl::is_void` meets the requirements of the `is_void` template defined in
/// the C++11 standard [meta.unary.cat], while `bslmf::IsVoid` was devised
/// before `is_void` was standardized.
///
/// The two meta-functions are functionally equivalent.  The major difference
/// between them is that the result for `bsl::is_void` is indicated by the
/// class member `value`, while the result for `bslmf::IsVoid` is indicated by
/// the class member `value`.
///
/// Note that `bsl::is_void` should be preferred over `bslmf::IsVoid`, and in
/// general, should be used by new components.
///
/// Also note that the template variable `is_void_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_void_v` is defined as an
/// `inline constexpr bool` variable.  Otherwise, if the compiler supports the
/// variable templates C++14 compiler feature, `bsl::is_void_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_isvoid-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Determine Whether a Type is the void Type {#bslmf_isvoid-example-1-determine-whether-a-type-is-the-void-type}
///
///
/// Suppose that we want to assert whether a particular type is the `void` type.
///
/// First, we create two `typedef`s -- the `void` type and another type:
/// @code
/// typedef int  MyType;
/// typedef void MyVoidType;
/// @endcode
/// Now, we instantiate the `bsl::is_void` template for each of the `typedef`s
/// and assert the `value` static data member of each instantiation:
/// @code
/// assert(false == bsl::is_void<MyType>::value);
/// assert(true  == bsl::is_void<MyVoidType>::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 as follows:
/// @code
/// #ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
///   assert(false == bsl::is_void_v<MyType>);
///   assert(true  == bsl::is_void_v<MyVoidType>);
/// #endif
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_isvoid
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
 
#include <bsls_compilerfeatures.h>
#include <bsls_keyword.h>
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bslmf_integralconstant.h>
#include <bslmf_removecv.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
 
 
namespace bsl {
 
                         // ==============
                         // struct is_void
                         // ==============
 
/// This `struct` template implements the `is_void` meta-function defined in
/// the C++11 standard [meta.unary.cat] to determine if the (template
/// parameter) `t_TYPE` is the (possibly cv-qualified) `void` type.  This
/// `struct` derives from `bsl::true_type` if `t_TYPE` is the `void` type,
/// and `bsl::false_type` otherwise.
template <class t_TYPE>
struct is_void : false_type {
};
 
/// This partial specialization of `is_void` derives from `bsl::true_type`
/// for when the (template parameter) `t_TYPE` is `void`.
template <>
struct is_void<void> : true_type {
};
 
/// This partial specialization of `is_void` derives from `bsl::true_type`
/// for when the (template parameter) `t_TYPE` is `const void`.
template <>
struct is_void<const void> : true_type {
};
 
/// This partial specialization of `is_void` derives from `bsl::true_type`
/// for when the (template parameter) `t_TYPE` is `volatile void`.
template <>
struct is_void<volatile void> : true_type {
};
 
/// This partial specialization of `is_void` derives from `bsl::true_type`
/// for when the (template parameter) `t_TYPE` is `const volatile void`.
template <>
struct is_void<const volatile void> : bsl::true_type {
};
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_VARIABLE_TEMPLATES
/// This template variable represents the result value of the `bsl::is_void`
/// meta-function.
template <class t_TYPE>
BSLS_KEYWORD_INLINE_VARIABLE constexpr bool is_void_v = is_void<t_TYPE>::value;
#endif
 
}  // close namespace bsl
 
 
namespace bslmf {
 
                        // ===================
                        // struct bslmf_IsVoid
                        // ===================
 
/// This `struct` template implements a meta-function to determine if the
/// (template parameter) `t_TYPE` is the (possibly cv-qualified) `void`
/// type.  This `struct` derives from `bsl::true_type` if `t_TYPE` is the
/// `void` type, and `bsl::false_type` otherwise.
///
/// Note that although this `struct` is functionally equivalent to
/// `bsl::is_void`, and the use of `bsl::is_void` should be preferred.
template <class t_TYPE>
struct IsVoid : bsl::is_void<t_TYPE>::type {
};
 
}  // close package namespace
 
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */