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132 lines
3.6 KiB
C++
132 lines
3.6 KiB
C++
/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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flow.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 FIT_GUARD_FUNCTION_FLOW_H
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#define FIT_GUARD_FUNCTION_FLOW_H
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/// flow
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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 `flow` function adaptor provides function composition. It is useful as
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/// an alternative to using the pipe operator `|` when chaining functions. It is
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/// similiar to [`compose`](compose.md) except the evaluation order is
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/// reversed. So, `flow(f, g)(0)` is equivalent to `g(f(0))`.
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///
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///
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/// Synopsis
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/// --------
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///
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/// template<class... Fs>
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/// constexpr flow_adaptor<Fs...> flow(Fs... fs);
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///
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/// Semantics
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/// ---------
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///
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/// assert(flow(f, g)(xs...) == g(f(xs...)));
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///
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/// Requirements
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/// ------------
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///
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/// Fs must be:
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///
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/// * [Callable](concepts.md#callable)
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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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/// struct increment
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/// {
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/// template<class T>
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/// T operator()(T x) const
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/// {
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/// return x + 1;
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/// }
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/// };
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///
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/// struct decrement
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/// {
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/// template<class T>
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/// T operator()(T x) const
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/// {
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/// return x - 1;
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/// }
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/// };
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///
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/// int r = flow(increment(), decrement(), increment())(3);
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/// assert(r == 4);
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///
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#include <fit/detail/callable_base.hpp>
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#include <fit/always.hpp>
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#include <fit/detail/delegate.hpp>
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#include <fit/detail/compressed_pair.hpp>
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#include <fit/detail/join.hpp>
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#include <tuple>
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#include <fit/detail/move.hpp>
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#include <fit/detail/make.hpp>
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#include <fit/detail/static_const_var.hpp>
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namespace fit { namespace detail {
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template<class F1, class F2>
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struct flow_kernel : detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>>
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{
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typedef detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>> base_type;
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FIT_INHERIT_CONSTRUCTOR(flow_kernel, base_type)
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FIT_RETURNS_CLASS(flow_kernel);
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template<class... Ts>
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constexpr FIT_SFINAE_RESULT(const detail::callable_base<F2>&, result_of<const detail::callable_base<F1>&, id_<Ts>...>)
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operator()(Ts&&... xs) const FIT_SFINAE_RETURNS
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(
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FIT_MANGLE_CAST(const detail::callable_base<F2>&)(FIT_CONST_THIS->second(xs...))(
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FIT_MANGLE_CAST(const detail::callable_base<F1>&)(FIT_CONST_THIS->first(xs...))(FIT_FORWARD(Ts)(xs)...)
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)
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);
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};
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}
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template<class F, class... Fs>
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struct flow_adaptor : detail::flow_kernel<F, FIT_JOIN(flow_adaptor, Fs...)>
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{
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typedef flow_adaptor fit_rewritable_tag;
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typedef FIT_JOIN(flow_adaptor, Fs...) tail;
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typedef detail::flow_kernel<F, tail> base;
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FIT_INHERIT_DEFAULT(flow_adaptor, base)
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template<class X, class... Xs, FIT_ENABLE_IF_CONVERTIBLE(X, F), FIT_ENABLE_IF_CONSTRUCTIBLE(tail, Xs...)>
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constexpr flow_adaptor(X&& f1, Xs&& ... fs)
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: base(FIT_FORWARD(X)(f1), tail(FIT_FORWARD(Xs)(fs)...))
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{}
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};
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template<class F>
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struct flow_adaptor<F> : detail::callable_base<F>
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{
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typedef flow_adaptor fit_rewritable_tag;
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FIT_INHERIT_DEFAULT(flow_adaptor, detail::callable_base<F>)
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template<class X, FIT_ENABLE_IF_CONVERTIBLE(X, detail::callable_base<F>)>
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constexpr flow_adaptor(X&& f1)
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: detail::callable_base<F>(FIT_FORWARD(X)(f1))
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{}
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};
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FIT_DECLARE_STATIC_VAR(flow, detail::make<flow_adaptor>);
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} // namespace fit
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#endif
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