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114 lines
3.0 KiB
C++
114 lines
3.0 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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result.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_RESULT_H
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#define FIT_GUARD_RESULT_H
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/// result
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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 `result` function adaptor sets the return type for the function, which
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/// can be useful when dealing with multiple overloads. Since the return type
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/// is no longer dependent on the parameters passed to the function, the
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/// `result_adaptor` provides a nested `result_type` that is the return type
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/// of the function.
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///
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/// Synopsis
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/// --------
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///
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/// template<class Result, class F>
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/// constexpr result_adaptor<Result, F> result(F f);
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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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/// * [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 id
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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;
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/// }
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/// };
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///
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/// auto int_result = fit::result<int>(id());
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/// static_assert(std::is_same<decltype(int_result(true)), int>::value, "Not the same type");
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///
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#include <fit/detail/callable_base.hpp>
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#include <fit/is_callable.hpp>
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#include <fit/always.hpp>
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#include <fit/reveal.hpp>
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namespace fit {
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template<class Result, class F>
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struct result_adaptor : detail::callable_base<F>
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{
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FIT_INHERIT_CONSTRUCTOR(result_adaptor, detail::callable_base<F>)
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typedef Result result_type;
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struct failure
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: failure_for<detail::callable_base<F>>
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{};
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template<class... Ts>
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constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
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{
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return always_ref(*this)(xs...);
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}
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template<class... Ts, class=typename std::enable_if<(fit::is_callable<F, Ts...>::value)>::type>
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constexpr result_type operator()(Ts&&... xs) const
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{
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return this->base_function(xs...)(FIT_FORWARD(Ts)(xs)...);
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};
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};
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template<class F>
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struct result_adaptor<void, F> : detail::callable_base<F>
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{
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FIT_INHERIT_CONSTRUCTOR(result_adaptor, detail::callable_base<F>)
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typedef void result_type;
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template<class... Ts>
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constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
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{
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return always_ref(*this)(xs...);
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}
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template<class... Ts, class=typename std::enable_if<(fit::is_callable<F, Ts...>::value)>::type>
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constexpr typename detail::holder<Ts...>::type operator()(Ts&&... xs) const
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{
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return (typename detail::holder<Ts...>::type)this->base_function(xs...)(FIT_FORWARD(Ts)(xs)...);
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};
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};
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// TODO: Make this a variable template in C++14
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template<class Result, class F>
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constexpr result_adaptor<Result, F> result(F f)
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{
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return result_adaptor<Result, F>(std::move(f));
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}
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} // namespace fit
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#endif
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