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113 lines
2.3 KiB
C++
113 lines
2.3 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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args.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_ARGS_H
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#define FIT_GUARD_FUNCTION_ARGS_H
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#include <fit/detail/seq.h>
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#include <fit/returns.h>
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#include <utility>
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/// args
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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 `args` returns a function object that returns the Nth argument passed
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/// to it. It actually starts at 1, so it is not the zero-based index of the
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/// argument.
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///
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/// Synopsis
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/// --------
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///
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/// template<class IntegralConstant>
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/// constexpr auto args(IntegralConstant);
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///
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///
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/// Example
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/// -------
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///
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/// assert(args(std::integral_constant<int, 3>())(1,2,3,4,5) == 3);
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///
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namespace fit {
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namespace detail {
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template<class T>
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struct perfect_ref
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{
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typedef T&& type;
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T&& value;
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constexpr perfect_ref(T&& x) : value(fit::forward<T>(x))
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{}
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};
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template<class T>
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constexpr perfect_ref<T> make_perfect_ref(T&& x)
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{
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return { fit::forward<T>(x) };
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}
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template<int N>
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struct ignore
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{
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template<class T>
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constexpr ignore(T&&...)
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{}
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};
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template<int... N>
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struct args_at
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{
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template<class T, class... Ts>
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constexpr auto operator()(ignore<N>..., T x, Ts...) const
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FIT_RETURNS(fit::forward<typename T::type>(x.value));
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};
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template<int... N>
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constexpr args_at<N...> make_args_at(seq<N...>)
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{
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return {};
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}
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template<int N, class... Ts>
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constexpr auto get_args(Ts&&... xs) FIT_RETURNS
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(
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make_args_at(typename gens<N>::type())(nullptr, make_perfect_ref(fit::forward<Ts>(xs))...)
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);
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template<class T, T N>
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struct args_f
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{
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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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get_args<N>(fit::forward<Ts>(xs)...)
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);
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};
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}
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// Deprecate
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template<int N, class... Ts>
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constexpr auto args(Ts&&... xs) FIT_RETURNS
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(
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detail::get_args<N>(fit::forward<Ts>(xs)...)
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);
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template<class IntegralConstant>
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constexpr detail::args_f<int, IntegralConstant::value> args(IntegralConstant)
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{
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return detail::args_f<int, IntegralConstant::value>();
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}
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}
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#endif
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