bslmf_booleantestable.h

Go to the documentation of this file.

/// @file bslmf_booleantestable.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_booleantestable.h                                            -*-C++-*-
#ifndef INCLUDED_BSLMF_BOOLEANTESTABLE
#define INCLUDED_BSLMF_BOOLEANTESTABLE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_booleantestable bslmf_booleantestable
/// @brief  Provide an exposition-only concept `boolean-testable`.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_booleantestable
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_booleantestable-purpose"> Purpose</a>
/// * <a href="#bslmf_booleantestable-classes"> Classes </a>
/// * <a href="#bslmf_booleantestable-description"> Description </a>
///   * <a href="#bslmf_booleantestable-usage"> Usage </a>
///     * <a href="#bslmf_booleantestable-example-1-implementing-a-concept-for-a-predicate-expression"> Example 1: Implementing a Concept for a Predicate (Boolean) Expression </a>
///
/// # Purpose {#bslmf_booleantestable-purpose}
/// Provide an exposition-only concept `boolean-testable`.
///
/// # Classes {#bslmf_booleantestable-classes}
///
/// -  bslmf::BooleanTestable: standard exposition-only `boolean-testable` concept
///
/// # Description {#bslmf_booleantestable-description}
/// This component provides a concept, `bslmf::BooleanTestable`,
/// that specifies the requirements on expressions that are convertible to
/// `bool` and for which the logical operators have the conventional semantics.
/// For more details, please refer to [concept.booleantestable] in the ISO C++20
/// Standard.
///
/// ## Usage {#bslmf_booleantestable-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Implementing a Concept for a Predicate (Boolean) Expression {#bslmf_booleantestable-example-1-implementing-a-concept-for-a-predicate-expression}
///
///
/// In the following example we use `bslmf::BooleanTestable` to implement a
/// concept to determine whether applying the `<` operator to a given type
/// produces an `if`-testable result.
/// @code
/// template <class t_TYPE>
/// concept LessComparable =
///     requires(t_TYPE v) {
///         { v < v } -> bslmf::BooleanTestable;
///     };
/// @endcode
/// Now types can be tested using this concept:
/// @code
/// static_assert(LessComparable<int>);
///
/// struct NonLessComparable { void operator<(NonLessComparable) {} };
/// static_assert(!LessComparable<NonLessComparable>);
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_booleantestable
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bsls_libraryfeatures.h>
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS
 
#include <concepts>
 
 
namespace bslmf {
 
template <class t_TYPE>
concept BooleanTestable_Impl = std::convertible_to<t_TYPE, bool>;
 
template <class t_TYPE>
concept BooleanTestable =
    // Specify the requirements on expressions that are convertible to 'bool'
    // and for which the logical operators have the conventional semantics.
    // Note that this is an implementation of the exposition-only concept
    // 'boolean-testable' defined by the ISO C++20 Standard
    // [concept.booleantestable].
    BooleanTestable_Impl<t_TYPE> &&
    requires(t_TYPE&& t) {
        { !static_cast<t_TYPE&&>(t) } -> BooleanTestable_Impl;
    };
 
}  // close package namespace
 
#endif  // BSLS_LIBRARYFEATURES_HAS_CPP20_CONCEPTS
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2023 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */