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+/*=============================================================================
+ Copyright (c) 2015 Paul Fultz II
+ apply_eval.h
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+
+#ifndef BOOST_HOF_GUARD_APPLY_EVAL_H
+#define BOOST_HOF_GUARD_APPLY_EVAL_H
+
+/// apply_eval
+/// ==========
+///
+/// Description
+/// -----------
+///
+/// The `apply_eval` function work like [`apply`](/include/boost/hof/apply), except it calls
+/// [`eval`](/include/boost/hof/eval) on each of its arguments. Each [`eval`](/include/boost/hof/eval) call is
+/// always ordered from left-to-right.
+///
+/// Synopsis
+/// --------
+///
+/// template<class F, class... Ts>
+/// constexpr auto apply_eval(F&& f, Ts&&... xs);
+///
+/// Semantics
+/// ---------
+///
+/// assert(apply_eval(f)(xs...) == f(eval(xs)...));
+///
+/// Requirements
+/// ------------
+///
+/// F must be:
+///
+/// * [ConstInvocable](ConstInvocable)
+///
+/// Ts must be:
+///
+/// * [EvaluatableFunctionObject](EvaluatableFunctionObject)
+///
+/// Example
+/// -------
+///
+/// #include <boost/hof.hpp>
+/// #include <cassert>
+///
+/// struct sum_f
+/// {
+/// template<class T, class U>
+/// T operator()(T x, U y) const
+/// {
+/// return x+y;
+/// }
+/// };
+///
+/// int main() {
+/// assert(boost::hof::apply_eval(sum_f(), []{ return 1; }, []{ return 2; }) == 3);
+/// }
+///
+
+#include <boost/hof/config.hpp>
+#include <boost/hof/returns.hpp>
+#include <boost/hof/detail/forward.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+#include <boost/hof/apply.hpp>
+#include <boost/hof/eval.hpp>
+
+#if BOOST_HOF_NO_ORDERED_BRACE_INIT
+#include <boost/hof/pack.hpp>
+#include <boost/hof/capture.hpp>
+#endif
+
+namespace boost { namespace hof {
+
+namespace detail {
+
+#if BOOST_HOF_NO_ORDERED_BRACE_INIT
+template<class R, class F, class Pack>
+constexpr R eval_ordered(const F& f, Pack&& p)
+{
+ return p(f);
+}
+
+template<class R, class F, class Pack, class T, class... Ts>
+constexpr R eval_ordered(const F& f, Pack&& p, T&& x, Ts&&... xs)
+{
+ 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)...);
+}
+#else
+template<class R>
+struct eval_helper
+{
+ R result;
+
+ template<class F, class... Ts>
+ constexpr eval_helper(const F& f, Ts&&... xs) : result(boost::hof::apply(f, BOOST_HOF_FORWARD(Ts)(xs)...))
+ {}
+};
+
+template<>
+struct eval_helper<void>
+{
+ int x;
+ template<class F, class... Ts>
+ constexpr eval_helper(const F& f, Ts&&... xs) : x((boost::hof::apply(f, BOOST_HOF_FORWARD(Ts)(xs)...), 0))
+ {}
+};
+#endif
+
+struct apply_eval_f
+{
+ template<class F, class... Ts, class R=decltype(
+ boost::hof::apply(std::declval<const F&>(), boost::hof::eval(std::declval<Ts>())...)
+ ),
+ class=typename std::enable_if<(!std::is_void<R>::value)>::type
+ >
+ 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))...))
+ {
+ return
+#if BOOST_HOF_NO_ORDERED_BRACE_INIT
+ boost::hof::detail::eval_ordered<R>
+ (f, boost::hof::pack(), BOOST_HOF_FORWARD(Ts)(xs)...);
+#else
+ boost::hof::detail::eval_helper<R>
+ {f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...}.result;
+#endif
+ }
+
+ template<class F, class... Ts, class R=decltype(
+ boost::hof::apply(std::declval<const F&>(), boost::hof::eval(std::declval<Ts>())...)
+ ),
+ class=typename std::enable_if<(std::is_void<R>::value)>::type
+ >
+ constexpr typename detail::holder<Ts...>::type
+ operator()(const F& f, Ts&&... xs) const BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(boost::hof::apply(f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...))
+ {
+ return (typename detail::holder<Ts...>::type)
+#if BOOST_HOF_NO_ORDERED_BRACE_INIT
+ boost::hof::detail::eval_ordered<R>
+ (f, boost::hof::pack(), BOOST_HOF_FORWARD(Ts)(xs)...);
+#else
+ boost::hof::detail::eval_helper<R>
+ {f, boost::hof::eval(BOOST_HOF_FORWARD(Ts)(xs))...};
+#endif
+ }
+};
+
+}
+
+BOOST_HOF_DECLARE_STATIC_VAR(apply_eval, detail::apply_eval_f);
+
+}} // namespace boost::hof
+
+#endif