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Diffstat (limited to 'boost/hana/if.hpp')
-rw-r--r-- | boost/hana/if.hpp | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/boost/hana/if.hpp b/boost/hana/if.hpp new file mode 100644 index 0000000000..f65b514be7 --- /dev/null +++ b/boost/hana/if.hpp @@ -0,0 +1,61 @@ +/*! +@file +Defines `boost::hana::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_IF_HPP +#define BOOST_HANA_IF_HPP + +#include <boost/hana/fwd/if.hpp> + +#include <boost/hana/concept/logical.hpp> +#include <boost/hana/config.hpp> +#include <boost/hana/core/dispatch.hpp> +#include <boost/hana/eval_if.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! @cond + template <typename Cond, typename Then, typename Else> + constexpr decltype(auto) if_t::operator()(Cond&& cond, Then&& then, Else&& else_) const { + using Bool = typename hana::tag_of<Cond>::type; + using If = BOOST_HANA_DISPATCH_IF(if_impl<Bool>, + hana::Logical<Bool>::value + ); + + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Logical<Bool>::value, + "hana::if_(cond, then, else) requires 'cond' to be a Logical"); + #endif + + return If::apply(static_cast<Cond&&>(cond), + static_cast<Then&&>(then), + static_cast<Else&&>(else_)); + } + //! @endcond + + namespace detail { + template <typename T> + struct hold { + T value; + constexpr T&& operator()() && { return static_cast<T&&>(value); } + }; + } + + template <typename L, bool condition> + struct if_impl<L, when<condition>> : default_ { + template <typename C, typename T, typename E> + static constexpr auto apply(C&& c, T&& t, E&& e) { + return hana::eval_if(static_cast<C&&>(c), + detail::hold<T&&>{static_cast<T&&>(t)}, + detail::hold<E&&>{static_cast<E&&>(e)} + ); + } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_IF_HPP |