/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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capture.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_CAPTURE_H
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#define BOOST_HOF_GUARD_CAPTURE_H
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#include <boost/hof/detail/callable_base.hpp>
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#include <boost/hof/detail/compressed_pair.hpp>
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#include <boost/hof/reveal.hpp>
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#include <boost/hof/pack.hpp>
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#include <boost/hof/always.hpp>
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#include <boost/hof/detail/move.hpp>
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#include <boost/hof/detail/result_type.hpp>
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/// capture
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/// =======
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///
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/// Description
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/// -----------
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///
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/// The `capture` function decorator is used to capture values in a function.
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/// It provides more flexibility in capturing than the lambda capture list in
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/// C++. It provides a way to do move and perfect capturing. The values
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/// captured are prepended to the argument list of the function that will be
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/// called.
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///
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/// Synopsis
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/// --------
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///
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/// // Capture by decaying each value
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/// template<class... Ts>
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/// constexpr auto capture(Ts&&... xs);
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///
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/// // Capture lvalues by reference and rvalue reference by reference
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/// template<class... Ts>
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/// constexpr auto capture_forward(Ts&&... xs);
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///
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/// // Capture lvalues by reference and rvalues by value.
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/// template<class... Ts>
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/// constexpr auto capture_basic(Ts&&... xs);
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///
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/// Semantics
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/// ---------
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///
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/// assert(capture(xs...)(f)(ys...) == f(xs..., ys...));
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///
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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///
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/// struct sum_f
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/// {
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/// template<class T, class U>
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/// T operator()(T x, U y) const
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/// {
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/// return x+y;
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/// }
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/// };
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///
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/// int main() {
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/// auto add_one = boost::hof::capture(1)(sum_f());
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/// assert(add_one(2) == 3);
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/// }
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///
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namespace boost { namespace hof {
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namespace detail {
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template<class F, class Pack>
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struct capture_invoke : detail::compressed_pair<detail::callable_base<F>, Pack>, detail::function_result_type<F>
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{
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typedef capture_invoke fit_rewritable1_tag;
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typedef detail::compressed_pair<detail::callable_base<F>, Pack> base;
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BOOST_HOF_INHERIT_CONSTRUCTOR(capture_invoke, base)
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template<class... Ts>
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constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
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{
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return this->first(xs...);
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}
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template<class... Ts>
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constexpr const Pack& get_pack(Ts&&...xs) const noexcept
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{
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return this->second(xs...);
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}
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template<class Failure, class... Ts>
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struct unpack_capture_failure
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{
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template<class... Us>
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struct apply
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{
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typedef typename Failure::template of<Us..., Ts...> type;
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};
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};
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struct capture_failure
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{
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template<class Failure>
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struct apply
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{
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template<class... Ts>
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struct of
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: Pack::template apply<unpack_capture_failure<Failure, Ts...>>::type
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{};
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};
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};
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struct failure
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: failure_map<capture_failure, detail::callable_base<F>>
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{};
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BOOST_HOF_RETURNS_CLASS(capture_invoke);
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template<class... Ts>
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constexpr BOOST_HOF_SFINAE_RESULT
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(
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typename result_of<decltype(boost::hof::pack_join),
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id_<const Pack&>,
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result_of<decltype(boost::hof::pack_forward), id_<Ts>...>
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>::type,
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id_<detail::callable_base<F>&&>
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)
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operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
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(
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boost::hof::pack_join
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(
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BOOST_HOF_MANGLE_CAST(const Pack&)(BOOST_HOF_CONST_THIS->get_pack(xs...)),
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boost::hof::pack_forward(BOOST_HOF_FORWARD(Ts)(xs)...)
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)
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(BOOST_HOF_RETURNS_C_CAST(detail::callable_base<F>&&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
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);
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};
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template<class Pack>
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struct capture_pack : Pack
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{
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BOOST_HOF_INHERIT_CONSTRUCTOR(capture_pack, Pack);
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BOOST_HOF_RETURNS_CLASS(capture_pack);
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// TODO: Should use rvalue ref qualifier
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template<class F>
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constexpr auto operator()(F f) const BOOST_HOF_SFINAE_RETURNS
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(
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capture_invoke<F, Pack>(BOOST_HOF_RETURNS_STATIC_CAST(F&&)(f),
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BOOST_HOF_RETURNS_C_CAST(Pack&&)(
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BOOST_HOF_RETURNS_STATIC_CAST(const Pack&)(*boost::hof::always(BOOST_HOF_CONST_THIS)(f))
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)
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)
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);
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};
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struct make_capture_pack_f
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{
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template<class Pack>
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constexpr capture_pack<Pack> operator()(Pack p) const
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BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(capture_pack<Pack>, Pack&&)
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{
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return capture_pack<Pack>(static_cast<Pack&&>(p));
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}
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};
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template<class F>
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struct capture_f
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{
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
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(
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BOOST_HOF_RETURNS_CONSTRUCT(make_capture_pack_f)()(BOOST_HOF_RETURNS_CONSTRUCT(F)()(BOOST_HOF_FORWARD(Ts)(xs)...))
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);
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};
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}
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BOOST_HOF_DECLARE_STATIC_VAR(capture_basic, detail::capture_f<detail::pack_basic_f>);
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BOOST_HOF_DECLARE_STATIC_VAR(capture_forward, detail::capture_f<detail::pack_forward_f>);
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BOOST_HOF_DECLARE_STATIC_VAR(capture, detail::capture_f<detail::pack_f>);
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}} // namespace boost::hof
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#endif
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