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/*!
@file
Defines `BOOST_HANA_DISPATCH_IF`.
@copyright Louis Dionne 2013-2017
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_DETAIL_DISPATCH_IF_HPP
#define BOOST_HANA_DETAIL_DISPATCH_IF_HPP
#include <boost/hana/config.hpp>
#include <type_traits>
BOOST_HANA_NAMESPACE_BEGIN
struct deleted_implementation {
template <typename ...T>
static constexpr auto apply(T&& ...) = delete;
};
//! @ingroup group-details
//! Dispatch to the given implementation method only when a condition is
//! satisfied.
//!
//! If the condition is satisfied, this macro is equivalent to the type
//! `IMPL`. Otherwise, it is equivalent to a type with a deleted static
//! function named `apply`. When a tag-dispatching error happens, the
//! condition should be false and the deleted static function `apply`
//! will prevent the compiler from generating too much garbage.
//!
//! @note
//! When `BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS` is defined, the
//! condition is always ignored and this macro expands to the
//! implementation only.
//!
//! @remark
//! This must be implemented as a macro, because we don't want the
//! condition to be evaluated at all when
//! `BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS` is defined.
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
#define BOOST_HANA_DISPATCH_IF(IMPL, ...) \
::std::conditional_t< \
(__VA_ARGS__), \
IMPL, \
::boost::hana::deleted_implementation \
> \
/**/
#else
#define BOOST_HANA_DISPATCH_IF(IMPL, ...) IMPL
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_DISPATCH_IF_HPP
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