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Diffstat (limited to 'boost/hof/apply_eval.hpp')
-rw-r--r-- | boost/hof/apply_eval.hpp | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/boost/hof/apply_eval.hpp b/boost/hof/apply_eval.hpp new file mode 100644 index 0000000000..2c0c265abf --- /dev/null +++ b/boost/hof/apply_eval.hpp @@ -0,0 +1,156 @@ +/*============================================================================= + 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 |