1/*============================================================================= 2 Copyright (c) 2015 Paul Fultz II 3 apply_eval.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_APPLY_EVAL_H 9#define BOOST_HOF_GUARD_APPLY_EVAL_H 10 11/// apply_eval 12/// ========== 13/// 14/// Description 15/// ----------- 16/// 17/// The `apply_eval` function work like [`apply`](/include/boost/hof/apply), except it calls 18/// [`eval`](/include/boost/hof/eval) on each of its arguments. Each [`eval`](/include/boost/hof/eval) call is 19/// always ordered from left-to-right. 20/// 21/// Synopsis 22/// -------- 23/// 24/// template<class F, class... Ts> 25/// constexpr auto apply_eval(F&& f, Ts&&... xs); 26/// 27/// Semantics 28/// --------- 29/// 30/// assert(apply_eval(f)(xs...) == f(eval(xs)...)); 31/// 32/// Requirements 33/// ------------ 34/// 35/// F must be: 36/// 37/// * [ConstInvocable](ConstInvocable) 38/// 39/// Ts must be: 40/// 41/// * [EvaluatableFunctionObject](EvaluatableFunctionObject) 42/// 43/// Example 44/// ------- 45/// 46/// #include <boost/hof.hpp> 47/// #include <cassert> 48/// 49/// struct sum_f 50/// { 51/// template<class T, class U> 52/// T operator()(T x, U y) const 53/// { 54/// return x+y; 55/// } 56/// }; 57/// 58/// int main() { 59/// assert(boost::hof::apply_eval(sum_f(), []{ return 1; }, []{ return 2; }) == 3); 60/// } 61/// 62 63#include <boost/hof/config.hpp> 64#include <boost/hof/returns.hpp> 65#include <boost/hof/detail/forward.hpp> 66#include <boost/hof/detail/static_const_var.hpp> 67#include <boost/hof/apply.hpp> 68#include <boost/hof/eval.hpp> 69 70#if BOOST_HOF_NO_ORDERED_BRACE_INIT 71#include <boost/hof/pack.hpp> 72#include <boost/hof/capture.hpp> 73#endif 74 75namespace boost { namespace hof { 76 77namespace detail { 78 79#if BOOST_HOF_NO_ORDERED_BRACE_INIT 80template<class R, class F, class Pack> 81constexpr R eval_ordered(const F& f, Pack&& p) 82{ 83 return p(f); 84} 85 86template<class R, class F, class Pack, class T, class... Ts> 87constexpr R eval_ordered(const F& f, Pack&& p, T&& x, Ts&&... xs) 88{ 89 return boost::hof::detail::eval_ordered<R>(f, boost::hof::pack_join(BOOST_HOF_FORWARD(Pack)(p), boost::hof::pack_forward(boost::hof::eval(x))), BOOST_HOF_FORWARD(Ts)(xs)...); 90} 91#else 92template<class R> 93struct eval_helper 94{ 95 R result; 96 97 template<class F, class... Ts> 98 constexpr eval_helper(const F& f, Ts&&... xs) : result(boost::hof::apply(f, BOOST_HOF_FORWARD(Ts)(xs)...)) 99 {} 100}; 101 102template<> 103struct eval_helper<void> 104{ 105 int x; 106 template<class F, class... Ts> 107 constexpr eval_helper(const F& f, Ts&&... xs) : x((boost::hof::apply(f, BOOST_HOF_FORWARD(Ts)(xs)...), 0)) 108 {} 109}; 110#endif 111 112struct apply_eval_f 113{ 114 template<class F, class... Ts, class R=decltype( 115 boost::hof::apply(std::declval<const F&>(), boost::hof::eval(std::declval<Ts>())...) 116 ), 117 class=typename std::enable_if<(!std::is_void<R>::value)>::type 118 > 119 constexpr R operator()(const F& f, Ts&&... xs) const BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(boost::hof::apply(f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...)) 120 { 121 return 122#if BOOST_HOF_NO_ORDERED_BRACE_INIT 123 boost::hof::detail::eval_ordered<R> 124 (f, boost::hof::pack(), BOOST_HOF_FORWARD(Ts)(xs)...); 125#else 126 boost::hof::detail::eval_helper<R> 127 {f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...}.result; 128#endif 129 } 130 131 template<class F, class... Ts, class R=decltype( 132 boost::hof::apply(std::declval<const F&>(), boost::hof::eval(std::declval<Ts>())...) 133 ), 134 class=typename std::enable_if<(std::is_void<R>::value)>::type 135 > 136 constexpr typename detail::holder<Ts...>::type 137 operator()(const F& f, Ts&&... xs) const BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(boost::hof::apply(f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...)) 138 { 139 return (typename detail::holder<Ts...>::type) 140#if BOOST_HOF_NO_ORDERED_BRACE_INIT 141 boost::hof::detail::eval_ordered<R> 142 (f, boost::hof::pack(), BOOST_HOF_FORWARD(Ts)(xs)...); 143#else 144 boost::hof::detail::eval_helper<R> 145 {f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...}; 146#endif 147 } 148}; 149 150} 151 152BOOST_HOF_DECLARE_STATIC_VAR(apply_eval, detail::apply_eval_f); 153 154}} // namespace boost::hof 155 156#endif 157