74 lines
2.1 KiB
C++
74 lines
2.1 KiB
C++
/*!
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@file
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Defines `boost::hana::flip`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FUNCTIONAL_FLIP_HPP
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#define BOOST_HANA_FUNCTIONAL_FLIP_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/create.hpp>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @ingroup group-functional
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//! Invoke a function with its two first arguments reversed.
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//!
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//! Specifically, `flip(f)` is a function such that
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//! @code
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//! flip(f)(x, y, z...) == f(y, x, z...)
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//! @endcode
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//!
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//! ### Example
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//! @include example/functional/flip.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto flip = [](auto&& f) {
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return [perfect-capture](auto&& x, auto&& y, auto&& ...z) -> decltype(auto) {
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return forwarded(f)(forwarded(y), forwarded(x), forwarded(z)...);
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};
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};
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#else
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template <typename F>
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struct flip_t {
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F f;
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template <typename X, typename Y, typename ...Z>
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constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) const& {
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return f(
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static_cast<Y&&>(y),
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static_cast<X&&>(x),
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static_cast<Z&&>(z)...
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);
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}
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template <typename X, typename Y, typename ...Z>
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constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) & {
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return f(
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static_cast<Y&&>(y),
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static_cast<X&&>(x),
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static_cast<Z&&>(z)...
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);
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}
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template <typename X, typename Y, typename ...Z>
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constexpr decltype(auto) operator()(X&& x, Y&& y, Z&& ...z) && {
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return std::move(f)(
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static_cast<Y&&>(y),
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static_cast<X&&>(x),
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static_cast<Z&&>(z)...
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);
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}
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};
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constexpr detail::create<flip_t> flip{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FUNCTIONAL_FLIP_HPP
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