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74 lines
1.8 KiB
C++
74 lines
1.8 KiB
C++
/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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eval.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_EVAL_H
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#define FIT_GUARD_EVAL_H
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/// eval
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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 `eval` function will evaluate a "thunk". This can be either a nullary
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/// function or it can be a unary function that takes the identity function as
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/// the first parameter(which is helpful to delay compile-time checking).
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/// Also, additional parameters can be passed to `eval` to delay
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/// compiliation(so that result can depend on template parameters).
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///
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/// Synopsis
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/// --------
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///
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/// template<class F, class... Ts>
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/// constexpr auto eval(F&& f, Ts&&...);
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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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/// * [EvaluatableFunctionObject](concepts.md#evaluatablefunctionobject)
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///
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/// Example
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/// -------
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///
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/// assert(fit::eval([]{ return 3; }) == 3);
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///
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#include <fit/always.hpp>
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#include <fit/identity.hpp>
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#include <fit/conditional.hpp>
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#include <fit/detail/result_of.hpp>
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namespace fit {
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namespace detail {
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struct simple_eval
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{
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template<class F, class... Ts>
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constexpr FIT_SFINAE_RESULT(F)
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operator()(F&& f, Ts&&...xs) const FIT_SFINAE_RETURNS
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(fit::always_ref(f)(xs...)());
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};
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struct id_eval
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{
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template<class F, class... Ts>
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constexpr FIT_SFINAE_RESULT(F, id_<decltype(fit::identity)>)
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operator()(F&& f, Ts&&...xs) const FIT_SFINAE_RETURNS
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(fit::always_ref(f)(xs...)(fit::identity));
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};
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}
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FIT_DECLARE_STATIC_VAR(eval, fit::conditional_adaptor<detail::simple_eval, detail::id_eval>);
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} // namespace fit
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#endif
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