1 /*============================================================================= 2 Copyright (c) 2015 Paul Fultz II 3 flip.h 4 Distributed under the Boost Software License, Version 1.0. (See accompanying 5 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6 ==============================================================================*/ 7 8 #ifndef BOOST_HOF_GUARD_FLIP_H 9 #define BOOST_HOF_GUARD_FLIP_H 10 11 /// flip 12 /// ==== 13 /// 14 /// Description 15 /// ----------- 16 /// 17 /// The `flip` function adaptor swaps the first two parameters. 18 /// 19 /// Synopsis 20 /// -------- 21 /// 22 /// template<class F> 23 /// flip_adaptor<F> flip(F f); 24 /// 25 /// Semantics 26 /// --------- 27 /// 28 /// assert(flip(f)(x, y, xs...) == f(y, x, xs...)); 29 /// 30 /// Requirements 31 /// ------------ 32 /// 33 /// F must be at least: 34 /// 35 /// * [BinaryInvocable](BinaryInvocable) 36 /// 37 /// Or: 38 /// 39 /// * [Invocable](Invocable) with more than two argurments 40 /// 41 /// And: 42 /// 43 /// * MoveConstructible 44 /// 45 /// Example 46 /// ------- 47 /// 48 /// #include <boost/hof.hpp> 49 /// #include <cassert> 50 /// 51 /// int main() { 52 /// int r = boost::hof::flip(boost::hof::_ - boost::hof::_)(2, 5); 53 /// assert(r == 3); 54 /// } 55 /// 56 57 #include <boost/hof/detail/callable_base.hpp> 58 #include <boost/hof/reveal.hpp> 59 #include <boost/hof/detail/make.hpp> 60 #include <boost/hof/detail/static_const_var.hpp> 61 62 namespace boost { namespace hof { 63 64 template<class F> 65 struct flip_adaptor : detail::callable_base<F> 66 { 67 typedef flip_adaptor fit_rewritable1_tag; 68 BOOST_HOF_INHERIT_CONSTRUCTOR(flip_adaptor, detail::callable_base<F>); 69 70 template<class... Ts> base_functionboost::hof::flip_adaptor71 constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const 72 { 73 return boost::hof::always_ref(*this)(xs...); 74 } 75 76 struct flip_failure 77 { 78 template<class Failure> 79 struct apply 80 { 81 template<class T, class U, class... Ts> 82 struct of 83 : Failure::template of<U, T, Ts...> 84 {}; 85 }; 86 }; 87 88 struct failure 89 : failure_map<flip_failure, detail::callable_base<F>> 90 {}; 91 92 BOOST_HOF_RETURNS_CLASS(flip_adaptor); 93 94 template<class T, class U, class... Ts> 95 constexpr BOOST_HOF_SFINAE_RESULT(const detail::callable_base<F>&, id_<U>, id_<T>, id_<Ts>...) 96 operator()(T&& x, U&& y, Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS 97 ( 98 (BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(xs...))) 99 (BOOST_HOF_FORWARD(U)(y), BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...) 100 ); 101 }; 102 103 BOOST_HOF_DECLARE_STATIC_VAR(flip, detail::make<flip_adaptor>); 104 105 }} // namespace boost::hof 106 107 #endif 108