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126 lines
3.8 KiB
126 lines
3.8 KiB
/*============================================================================= |
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Copyright (c) 2015 Paul Fultz II |
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combine.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_COMBINE_H |
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#define BOOST_HOF_GUARD_COMBINE_H |
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/// combine |
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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 `combine` function adaptor combines several functions together with |
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/// their arguments. It essentially zips each function with an argument before |
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/// calling the main function. |
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/// |
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/// Synopsis |
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/// -------- |
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/// |
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/// template<class F, class... Gs> |
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/// constexpr combine_adaptor<F, Gs...> combine(F f, Gs... gs); |
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/// |
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/// Semantics |
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/// --------- |
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/// |
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/// assert(combine(f, gs...)(xs...) == f(gs(xs)...)); |
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/// |
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/// Requirements |
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/// ------------ |
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/// |
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/// F and Gs must be: |
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/// |
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/// * [ConstInvocable](ConstInvocable) |
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/// * MoveConstructible |
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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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/// #include <tuple> |
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/// #include <utility> |
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/// |
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/// int main() { |
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/// auto f = boost::hof::combine( |
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/// boost::hof::construct<std::tuple>(), |
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/// boost::hof::capture(1)(boost::hof::construct<std::pair>()), |
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/// boost::hof::capture(2)(boost::hof::construct<std::pair>())); |
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/// assert(f(3, 7) == std::make_tuple(std::make_pair(1, 3), std::make_pair(2, 7))); |
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/// } |
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/// |
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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/callable_base.hpp> |
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#include <boost/hof/detail/make.hpp> |
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namespace boost { namespace hof { namespace detail { |
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template<class S, class F, class... Gs> |
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struct combine_adaptor_base; |
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template<std::size_t... Ns, class F, class... Gs> |
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struct combine_adaptor_base<seq<Ns...>, F, Gs...> |
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: F, pack_base<seq<Ns...>, Gs...> |
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{ |
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typedef pack_base<seq<Ns...>, Gs...> base_type; |
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BOOST_HOF_INHERIT_DEFAULT(combine_adaptor_base, base_type, F) |
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template<class X, class... Xs, |
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BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(F, X), |
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BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(base_type, Xs...)> |
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constexpr combine_adaptor_base(X&& x, Xs&&... xs) |
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: F(BOOST_HOF_FORWARD(X)(x)), base_type(BOOST_HOF_FORWARD(Xs)(xs)...) |
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{} |
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template<class... Ts> |
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constexpr const F& base_function(Ts&&... xs) const |
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{ |
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return boost::hof::always_ref(*this)(xs...); |
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} |
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BOOST_HOF_RETURNS_CLASS(combine_adaptor_base); |
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// Result needs to be calculated in a separate class to avoid confusing the |
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// compiler on MSVC |
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#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION |
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template<class... Ts> |
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struct combine_result |
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: result_of<const F&, result_of<const Gs&, id_<Ts>>...> |
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{}; |
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#endif |
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template<class... Ts> |
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#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION |
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constexpr typename combine_result<Ts...>::type |
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#else |
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constexpr auto |
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#endif |
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operator()(Ts&&... xs) const BOOST_HOF_SFINAE_MANUAL_RETURNS |
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( |
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(BOOST_HOF_MANGLE_CAST(const F&)(BOOST_HOF_CONST_THIS->base_function(xs...))) |
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(boost::hof::alias_value<pack_tag<seq<Ns>, Gs...>, Gs>(*BOOST_HOF_CONST_THIS, xs)(BOOST_HOF_FORWARD(Ts)(xs))...) |
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); |
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}; |
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} |
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template<class F, class... Gs> |
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struct combine_adaptor |
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: detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...> |
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{ |
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typedef detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...> base_type; |
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BOOST_HOF_INHERIT_CONSTRUCTOR(combine_adaptor, base_type) |
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}; |
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BOOST_HOF_DECLARE_STATIC_VAR(combine, detail::make<combine_adaptor>); |
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}} // namespace boost::hof |
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#endif
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