/*!
* \file detection.h
* \brief Detection idiom based on WG21's N4502[1] from Walter E. Brown
*
* [1]: www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf
*
* Copyright (C) 2018-2019 Christos Choutouridis
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see .
*/
#ifndef __utl_meta_detection_h__
#define __utl_meta_detection_h__
#include
#include
#include
/*!
* \ingroup meta
* \defgroup detection
* Detection idiom support header.
*/
//! @{
namespace utl {
namespace meta {
/*!
* void_t meta-function that maps a sequence of any types to the type void
*/
//! @{
#if defined(UTL_WORKAROUND_CWG_1558)
template
struct void_ {
using type = void;
};
//! void_t type alias
template
using void_t = eval>;
#else
//! void_ type alias
template using void_ = void;
//! void_t type alias
template using void_t = void;
#endif
//! @}
/*!
* Not a type to use in detected idiom
*/
struct nat_ {
nat_() = delete;
~nat_() = delete;
nat_(nat_ const&) = delete;
void operator = (nat_ const&) = delete;
};
//! Detector for detection idiom
//! @{
namespace detail {
template class Op, typename... Args>
struct detector {
using detected = false_;
using type = Default;
};
template class Op, typename... Args>
struct detector >, Op, Args...> {
using detected = true_;
using type = Op;
};
//! helper for detected_or_t
template class Op, typename... Args>
using detected_or = detector;
} // namespace detail
//! @}
/*!
* detection interface
*/
//! @{
/*!
* Checks if Op is a valid expression without evaluating it.
*
* \param Op a meta-callback function to pass Args...
* \param Args... types to pass to Op for checking
* \return status of the operation [bool_]
* \arg true_ if Op is valid expression
* \arg false_ if Op is not valid
*
* \example
* \code
* // archetypal alias for a copy assignment operation
* template< class T >
* using copy_assign_t = decltype( declval() = declval() );
*
* template< class T >
* using is_copy_assignable = is_detected< T, copy_assign_t >;
* \endcode
*/
template class Op, typename... Args>
using is_detected = typename detail::detector::detected;
//! Detection predicate
template< template class Op, typename... Args>
constexpr bool is_detected_v = is_detected::value;
//! @}
/*!
* Detection idiom toolkit
*/
//! @{
//! evaluates to evaluation of Op if it's valid and to nat_ if not
template class Op, typename... Args>
using detected_t = eval <
detail::detector
>;
//! evaluates to evaluation of Op if it's valid and to \p Default if not
template class Op, typename... Args>
using detected_or_t = eval <
detail::detected_or
>;
//! evaluates to true_ if evaluation of Op is \p Expected and to false_ if not
template class Op, typename... Args >
using is_detected_exact = same_ >;
//! evaluates to true if evaluation of Op is \p Expected and to false if not
template class Op, typename... Args >
constexpr bool is_detected_exact_v = is_detected_exact< Expected, Op, Args...>::value;
//! evaluates to true_ if evaluation of Op is convertible to \p To
//! and to false_ if not
template class Op, typename... Args >
using is_detected_convertible = std::is_convertible< detected_t, To >;
//! evaluates to true if evaluation of Op is convertible to \p To
//! and to false if not
template class Op, typename... Args >
constexpr bool is_detected_convertible_v =
is_detected_convertible::value;
//! @}
}}
//!@}
#endif /* __utl_meta_detection_h__ */