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292 lines
8.1 KiB
292 lines
8.1 KiB
/*============================================================================= |
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Copyright (c) 2012 Paul Fultz II |
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partial.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_FUNCTION_PARTIAL_H |
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#define BOOST_HOF_GUARD_FUNCTION_PARTIAL_H |
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/// partial |
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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 `partial` function adaptor allows partial application of the function. |
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/// If the function can not be called with all the parameters, it will return |
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/// another function. It will repeatedly do this until the function can |
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/// finally be called. By default, `partial` captures all of its variables by |
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/// value, just like bind. As such all parameters must be `MoveConstructible` |
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/// when the function is aprtial application. `std::ref` can be used to |
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/// capture references instead. |
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/// |
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/// Synopsis |
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/// -------- |
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/// |
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/// template<class F> |
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/// constexpr partial_adaptor<F> partial(F f); |
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/// |
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/// Semantics |
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/// --------- |
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/// |
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/// assert(partial(f)(xs...)(ys...) == f(xs..., ys...)); |
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/// |
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/// Requirements |
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/// ------------ |
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/// |
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/// F 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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/// using namespace boost::hof; |
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/// |
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/// struct sum |
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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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/// assert(3 == partial(sum())(1)(2)); |
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/// } |
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/// |
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/// References |
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/// ---------- |
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/// |
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/// * [Partial application](https://en.wikipedia.org/wiki/Partial_application) |
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/// * [Currying](https://en.wikipedia.org/wiki/Currying) |
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/// |
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#include <boost/hof/first_of.hpp> |
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#include <boost/hof/static.hpp> |
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#include <boost/hof/pipable.hpp> |
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#include <boost/hof/detail/make.hpp> |
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#include <boost/hof/detail/static_const_var.hpp> |
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namespace boost { namespace hof { |
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// TODO: Get rid of sequence parameter |
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// Forward declare partial_adaptor, since it will be used below |
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template<class F, class Pack=void > |
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struct partial_adaptor; |
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BOOST_HOF_DECLARE_STATIC_VAR(partial, detail::make<partial_adaptor>); |
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namespace detail { |
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template<class Derived, class F, class Pack> |
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struct partial_adaptor_invoke |
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{ |
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template<class... Ts> |
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constexpr const F& get_function(Ts&&...) const noexcept |
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{ |
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return static_cast<const F&>(static_cast<const Derived&>(*this)); |
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} |
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template<class... Ts> |
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constexpr const Pack& get_pack(Ts&&...) const noexcept |
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{ |
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return static_cast<const Pack&>(static_cast<const Derived&>(*this)); |
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} |
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BOOST_HOF_RETURNS_CLASS(partial_adaptor_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_<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(F&&)(BOOST_HOF_CONST_THIS->get_function(xs...))) |
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); |
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}; |
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#ifdef _MSC_VER |
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#define BOOST_HOF_PARTIAL_RETURNS(...) -> decltype(__VA_ARGS__) { return (__VA_ARGS__); } |
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#else |
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#define BOOST_HOF_PARTIAL_RETURNS BOOST_HOF_SFINAE_RETURNS |
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#endif |
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template<class Derived, class F, class Pack> |
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struct partial_adaptor_join |
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{ |
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template<class... Ts> |
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constexpr const F& get_function(Ts&&...) const noexcept |
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{ |
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return static_cast<const F&>(static_cast<const Derived&>(*this)); |
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} |
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template<class... Ts> |
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constexpr const Pack& get_pack(Ts&&...) const noexcept |
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{ |
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return static_cast<const Pack&>(static_cast<const Derived&>(*this)); |
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} |
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BOOST_HOF_RETURNS_CLASS(partial_adaptor_join); |
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template<class... Ts, class=typename std::enable_if< |
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((sizeof...(Ts) + Pack::fit_function_param_limit::value) < function_param_limit<F>::value) |
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>::type> |
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constexpr auto operator()(Ts&&... xs) const |
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#ifdef _MSC_VER |
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// Workaround ICE on MSVC |
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noexcept(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(F, F&&) && noexcept(boost::hof::pack_join(std::declval<const Pack&>(), boost::hof::pack(BOOST_HOF_FORWARD(Ts)(xs)...)))) |
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#endif |
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BOOST_HOF_PARTIAL_RETURNS |
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( |
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boost::hof::partial |
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( |
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BOOST_HOF_RETURNS_C_CAST(F&&)(BOOST_HOF_CONST_THIS->get_function(xs...)), |
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boost::hof::pack_join(BOOST_HOF_MANGLE_CAST(const Pack&)(BOOST_HOF_CONST_THIS->get_pack(xs...)), boost::hof::pack(BOOST_HOF_FORWARD(Ts)(xs)...)) |
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) |
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); |
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}; |
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template<class Derived, class F> |
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struct partial_adaptor_pack |
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{ |
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constexpr partial_adaptor_pack() noexcept |
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{} |
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template<class... Ts> |
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constexpr const F& get_function(Ts&&...) const noexcept |
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{ |
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return static_cast<const F&>(static_cast<const Derived&>(*this)); |
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} |
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BOOST_HOF_RETURNS_CLASS(partial_adaptor_pack); |
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template<class... Ts, class=typename std::enable_if< |
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(sizeof...(Ts) < function_param_limit<F>::value) |
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>::type> |
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constexpr auto operator()(Ts&&... xs) const |
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#ifdef _MSC_VER |
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// Workaround ICE on MSVC |
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noexcept(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(F, F&&) && noexcept(boost::hof::pack(BOOST_HOF_FORWARD(Ts)(xs)...))) |
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#endif |
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BOOST_HOF_PARTIAL_RETURNS |
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( |
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boost::hof::partial |
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( |
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BOOST_HOF_RETURNS_C_CAST(F&&)(BOOST_HOF_CONST_THIS->get_function(xs...)), |
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boost::hof::pack(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 Pack> |
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struct partial_adaptor_base |
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{ |
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typedef basic_first_of_adaptor |
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< |
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partial_adaptor_invoke<partial_adaptor<F, Pack>, F, Pack>, |
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partial_adaptor_join<partial_adaptor<F, Pack>, F, Pack> |
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> type; |
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}; |
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template<class Derived, class F> |
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struct partial_adaptor_pack_base |
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{ |
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typedef basic_first_of_adaptor |
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< |
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F, |
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partial_adaptor_pack<Derived, F> |
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> type; |
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}; |
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} |
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template<class F, class Pack> |
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struct partial_adaptor : detail::partial_adaptor_base<F, Pack>::type, F, Pack |
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{ |
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typedef typename detail::partial_adaptor_base<F, Pack>::type base; |
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typedef partial_adaptor fit_rewritable1_tag; |
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template<class... Ts> |
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constexpr const F& base_function(Ts&&...) const noexcept |
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{ |
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return *this; |
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} |
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constexpr const Pack& get_pack() const noexcept |
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{ |
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return *this; |
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} |
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using base::operator(); |
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BOOST_HOF_INHERIT_DEFAULT(partial_adaptor, base, F, Pack); |
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template<class X, class S> |
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constexpr partial_adaptor(X&& x, S&& seq) |
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BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(F, X&&) && BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(Pack, S&&)) |
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: F(BOOST_HOF_FORWARD(X)(x)), Pack(BOOST_HOF_FORWARD(S)(seq)) |
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{} |
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}; |
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template<class F> |
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struct partial_adaptor<F, void> : detail::partial_adaptor_pack_base<partial_adaptor<F, void>, detail::callable_base<F>>::type |
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{ |
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typedef typename detail::partial_adaptor_pack_base<partial_adaptor<F, void>, detail::callable_base<F>>::type base; |
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typedef partial_adaptor fit_rewritable1_tag; |
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template<class... Ts> |
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constexpr const detail::callable_base<F>& base_function(Ts&&...) const noexcept |
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{ |
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return *this; |
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} |
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using base::operator(); |
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BOOST_HOF_INHERIT_CONSTRUCTOR(partial_adaptor, base); |
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}; |
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// Make partial_adaptor work with pipable_adaptor by removing its pipableness |
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template<class F> |
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struct partial_adaptor<pipable_adaptor<F>, void> |
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: partial_adaptor<F, void> |
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{ |
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typedef partial_adaptor<F, void> base; |
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typedef partial_adaptor fit_rewritable1_tag; |
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BOOST_HOF_INHERIT_CONSTRUCTOR(partial_adaptor, base); |
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}; |
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template<class F> |
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struct partial_adaptor<static_<pipable_adaptor<F>>, void> |
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: partial_adaptor<F, void> |
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{ |
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typedef partial_adaptor<F, void> base; |
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typedef partial_adaptor fit_rewritable1_tag; |
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BOOST_HOF_INHERIT_CONSTRUCTOR(partial_adaptor, base); |
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}; |
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}} // namespace boost::hof |
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#endif
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