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121 lines
2.6 KiB
C++
121 lines
2.6 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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arg.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.hpp>
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#include <fit/returns.hpp>
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#include <fit/detail/static_const_var.hpp>
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#include <utility>
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/// arg
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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 `arg` function returns a function object that returns the Nth argument
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/// passed to it. It actually starts at 1, so it is not the zero-based index
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/// of the 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 arg(IntegralConstant);
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///
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/// template<std::size_t N, class... Ts>
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/// constexpr auto arg_c(Ts&&...);
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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(arg(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<std::size_t 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<std::size_t... 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<std::size_t... 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<std::size_t 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 make_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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struct arg_f
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{
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template<class IntegralConstant>
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constexpr make_args_f<std::size_t, IntegralConstant::value> operator()(IntegralConstant) const
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{
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return make_args_f<std::size_t, IntegralConstant::value>();
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}
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};
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}
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template<std::size_t N, class... Ts>
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constexpr auto arg_c(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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FIT_DECLARE_STATIC_VAR(arg, detail::arg_f);
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} // namespace fit
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#endif
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