1/*!
2@file
3Defines `boost::hana::if_`.
4
5Copyright Louis Dionne 2013-2022
6Distributed 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_IF_HPP
11#define BOOST_HANA_IF_HPP
12
13#include <boost/hana/fwd/if.hpp>
14
15#include <boost/hana/concept/logical.hpp>
16#include <boost/hana/config.hpp>
17#include <boost/hana/core/dispatch.hpp>
18#include <boost/hana/eval_if.hpp>
19
20
21namespace boost { namespace hana {
22 //! @cond
23 template <typename Cond, typename Then, typename Else>
24 constexpr decltype(auto) if_t::operator()(Cond&& cond, Then&& then_, Else&& else_) const {
25 using Bool = typename hana::tag_of<Cond>::type;
26 using If = BOOST_HANA_DISPATCH_IF(if_impl<Bool>,
27 hana::Logical<Bool>::value
28 );
29
30 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
31 static_assert(hana::Logical<Bool>::value,
32 "hana::if_(cond, then, else) requires 'cond' to be a Logical");
33 #endif
34
35 return If::apply(static_cast<Cond&&>(cond),
36 static_cast<Then&&>(then_),
37 static_cast<Else&&>(else_));
38 }
39 //! @endcond
40
41 namespace detail {
42 template <typename T>
43 struct hold {
44 T value;
45 constexpr T&& operator()() && { return static_cast<T&&>(value); }
46 };
47 }
48
49 template <typename L, bool condition>
50 struct if_impl<L, when<condition>> : default_ {
51 template <typename C, typename T, typename E>
52 static constexpr auto apply(C&& c, T&& t, E&& e) {
53 return hana::eval_if(static_cast<C&&>(c),
54 detail::hold<T&&>{static_cast<T&&>(t)},
55 detail::hold<E&&>{static_cast<E&&>(e)}
56 );
57 }
58 };
59}} // end namespace boost::hana
60
61#endif // !BOOST_HANA_IF_HPP
62

source code of boost/libs/hana/include/boost/hana/if.hpp