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Diffstat (limited to 'boost/hana/detail/dispatch_if.hpp')
| -rw-r--r-- | boost/hana/detail/dispatch_if.hpp | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/boost/hana/detail/dispatch_if.hpp b/boost/hana/detail/dispatch_if.hpp new file mode 100644 index 0000000000..88073fa7a2 --- /dev/null +++ b/boost/hana/detail/dispatch_if.hpp @@ -0,0 +1,56 @@ +/*! +@file +Defines `BOOST_HANA_DISPATCH_IF`. + +@copyright Louis Dionne 2013-2016 +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 |