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130 lines
3.0 KiB
C++
130 lines
3.0 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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compose.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_COMPOSE_H
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#define FIT_GUARD_FUNCTION_COMPOSE_H
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/// compose
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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 `compose` function adaptor provides function composition. It produces
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/// a function object that composes a set of functions, ie the output of one
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/// function becomes the input of the second function. So, `compose(f, g)(0)`
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/// is equivalent to `f(g(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 compose_adaptor<Fs...> compose(Fs... fs);
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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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/// FunctionObject
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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 = compose(increment(), decrement(), increment())(3);
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/// assert(r == 4);
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///
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#include <fit/returns.h>
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#include <fit/always.h>
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#include <fit/detail/delegate.h>
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#include <fit/detail/join.h>
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#include <tuple>
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#include <fit/detail/move.h>
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namespace fit { namespace detail {
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// TODO: Try to use inheritance but make each base class unique
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template<class F1, class F2>
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struct compose_kernel
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{
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F1 f1;
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F2 f2;
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constexpr compose_kernel()
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{}
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template<class A, class B>
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constexpr compose_kernel(A&& f1, B&& f2)
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: f1(fit::forward<A>(f1)), f2(fit::forward<B>(f2))
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{}
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FIT_RETURNS_CLASS(compose_kernel);
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const FIT_RETURNS
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(
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FIT_CONST_THIS->f1(FIT_CONST_THIS->f2(fit::forward<Ts>(xs)...))
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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 compose_adaptor : detail::compose_kernel<F, FIT_JOIN(compose_adaptor, Fs...)>
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{
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typedef FIT_JOIN(compose_adaptor, Fs...) tail;
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typedef detail::compose_kernel<F, tail> base;
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constexpr compose_adaptor() {}
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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 compose_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 compose_adaptor<F> : F
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{
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constexpr compose_adaptor() {}
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template<class X, FIT_ENABLE_IF_CONVERTIBLE(X, F)>
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constexpr compose_adaptor(X&& f1)
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: F(fit::forward<X>(f1))
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{}
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};
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template<class... Fs>
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constexpr FIT_JOIN(compose_adaptor, Fs...) compose(Fs... fs)
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{
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return FIT_JOIN(compose_adaptor, Fs...)(fit::move(fs)...);
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}
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}
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#endif
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