1/*!
2@file
3Defines `boost::hana::flip`.
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_FUNCTIONAL_FLIP_HPP
11#define BOOST_HANA_FUNCTIONAL_FLIP_HPP
12
13#include <boost/hana/config.hpp>
14#include <boost/hana/detail/create.hpp>
15
16#include <utility>
17
18
19namespace boost { namespace hana {
20 //! @ingroup group-functional
21 //! Invoke a function with its two first arguments reversed.
22 //!
23 //! Specifically, `flip(f)` is a function such that
24 //! @code
25 //! flip(f)(x, y, z...) == f(y, x, z...)
26 //! @endcode
27 //!
28 //! ### Example
29 //! @include example/functional/flip.cpp
30#ifdef BOOST_HANA_DOXYGEN_INVOKED
31 constexpr auto flip = [](auto&& f) {
32 return [perfect-capture](auto&& x, auto&& y, auto&& ...z) -> decltype(auto) {
33 return forwarded(f)(forwarded(y), forwarded(x), forwarded(z)...);
34 };
35 };
36#else
37 template <typename F>
38 struct flip_t {
39 F f;
40
41 template <typename X, typename Y, typename ...Z>
42 constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) const& {
43 return f(
44 static_cast<Y&&>(y),
45 static_cast<X&&>(x),
46 static_cast<Z&&>(z)...
47 );
48 }
49
50 template <typename X, typename Y, typename ...Z>
51 constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) & {
52 return f(
53 static_cast<Y&&>(y),
54 static_cast<X&&>(x),
55 static_cast<Z&&>(z)...
56 );
57 }
58
59 template <typename X, typename Y, typename ...Z>
60 constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) && {
61 return std::move(f)(
62 static_cast<Y&&>(y),
63 static_cast<X&&>(x),
64 static_cast<Z&&>(z)...
65 );
66 }
67 };
68
69 BOOST_HANA_INLINE_VARIABLE constexpr detail::create<flip_t> flip{};
70#endif
71}} // end namespace boost::hana
72
73#endif // !BOOST_HANA_FUNCTIONAL_FLIP_HPP
74

source code of boost/libs/hana/include/boost/hana/functional/flip.hpp