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124 lines
2.9 KiB
C++
124 lines
2.9 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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/// * [ConstCallable](ConstCallable)
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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 <fit.hpp>
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/// #include <cassert>
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/// using namespace fit;
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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 main() {
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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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///
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/// References
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/// ----------
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///
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/// * [Function composition](https://en.wikipedia.org/wiki/Function_composition)
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///
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#include <fit/detail/builder.hpp>
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#include <fit/detail/builder/fold.hpp>
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#include <fit/reveal.hpp>
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namespace fit { namespace detail {
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struct flow_adaptor_base
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{
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template<class F, class G>
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struct base
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{
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struct flow_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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: Failure::template of<decltype(std::declval<F>()(std::declval<Ts>()...))>
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{};
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};
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};
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struct failure
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: with_failures<failure_map<flow_failure, G>, failure_for<F>>
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{};
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};
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struct apply
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{
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template<class F1, class F2, class... Ts>
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constexpr FIT_SFINAE_RESULT(const F1&, result_of<const F2&, id_<Ts>...>)
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operator()(F1&& f1, F2&& f2, Ts && ... xs) const
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FIT_SFINAE_RETURNS
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(
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FIT_FORWARD(F2)(f2)(FIT_FORWARD(F1)(f1)(FIT_FORWARD(Ts)(xs)...))
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);
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};
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};
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}
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FIT_DECLARE_ADAPTOR(flow, detail::fold_adaptor_builder<detail::flow_adaptor_base>)
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} // namespace fit
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#endif
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