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 Hu Chunming
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/*!
@file
Defines `boost::hana::flip`.
Copyright Louis Dionne 2013-2022
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_FUNCTIONAL_FLIP_HPP
#define BOOST_HANA_FUNCTIONAL_FLIP_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/detail/create.hpp>
#include <utility>
namespace boost { namespace hana {
//! @ingroup group-functional
//! Invoke a function with its two first arguments reversed.
//!
//! Specifically, `flip(f)` is a function such that
//! @code
//! flip(f)(x, y, z...) == f(y, x, z...)
//! @endcode
//!
//! ### Example
//! @include example/functional/flip.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto flip = [](auto&& f) {
return [perfect-capture](auto&& x, auto&& y, auto&& ...z) -> decltype(auto) {
return forwarded(f)(forwarded(y), forwarded(x), forwarded(z)...);
};
};
#else
template <typename F>
struct flip_t {
F f;
template <typename X, typename Y, typename ...Z>
constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) const& {
return f(
static_cast<Y&&>(y),
static_cast<X&&>(x),
static_cast<Z&&>(z)...
);
}
template <typename X, typename Y, typename ...Z>
constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) & {
return f(
static_cast<Y&&>(y),
static_cast<X&&>(x),
static_cast<Z&&>(z)...
);
}
template <typename X, typename Y, typename ...Z>
constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) && {
return std::move(f)(
static_cast<Y&&>(y),
static_cast<X&&>(x),
static_cast<Z&&>(z)...
);
}
};
BOOST_HANA_INLINE_VARIABLE constexpr detail::create<flip_t> flip{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FUNCTIONAL_FLIP_HPP
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