projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Defines `BOOST_HANA_DISPATCH_IF`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 6 | Distributed under the Boost Software License, Version 1.0. | |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 8 | */ | |
| 9 | ||
| 10 | #ifndef BOOST_HANA_DETAIL_DISPATCH_IF_HPP | |
| 11 | #define BOOST_HANA_DETAIL_DISPATCH_IF_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | ||
| 15 | #include <type_traits> | |
| 16 | ||
| 17 | ||
| 18 | BOOST_HANA_NAMESPACE_BEGIN | |
| 19 | struct deleted_implementation { | |
| 20 | template <typename ...T> | |
| 21 | static constexpr auto apply(T&& ...) = delete; | |
| 22 | }; | |
| 23 | ||
| 24 | //! @ingroup group-details | |
| 25 | //! Dispatch to the given implementation method only when a condition is | |
| 26 | //! satisfied. | |
| 27 | //! | |
| 28 | //! If the condition is satisfied, this macro is equivalent to the type | |
| 29 | //! `IMPL`. Otherwise, it is equivalent to a type with a deleted static | |
| 30 | //! function named `apply`. When a tag-dispatching error happens, the | |
| 31 | //! condition should be false and the deleted static function `apply` | |
| 32 | //! will prevent the compiler from generating too much garbage. | |
| 33 | //! | |
| 34 | //! @note | |
| 35 | //! When `BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS` is defined, the | |
| 36 | //! condition is always ignored and this macro expands to the | |
| 37 | //! implementation only. | |
| 38 | //! | |
| 39 | //! @remark | |
| 40 | //! This must be implemented as a macro, because we don't want the | |
| 41 | //! condition to be evaluated at all when | |
| 42 | //! `BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS` is defined. | |
| 43 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
| 44 | #define BOOST_HANA_DISPATCH_IF(IMPL, ...) \ | |
| 45 | ::std::conditional_t< \ | |
| 46 | (__VA_ARGS__), \ | |
| 47 | IMPL, \ | |
| 48 | ::boost::hana::deleted_implementation \ | |
| 49 | > \ | |
| 50 | /**/ | |
| 51 | #else | |
| 52 | #define BOOST_HANA_DISPATCH_IF(IMPL, ...) IMPL | |
| 53 | #endif | |
| 54 | BOOST_HANA_NAMESPACE_END | |
| 55 | ||
| 56 | #endif // !BOOST_HANA_DETAIL_DISPATCH_IF_HPP |