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79 lines
2.0 KiB
C++
79 lines
2.0 KiB
C++
/**
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* \file libimp/generic.h
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* \author mutouyun (orz@orzz.org)
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* \brief Tools for generic programming.
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* \date 2022-03-01
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*/
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#pragma once
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#include <utility>
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#include <type_traits>
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#include "libimp/def.h"
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#include "libimp/detect_plat.h"
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LIBIMP_NAMESPACE_BEG_
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/**
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* \brief Utility metafunction that maps a sequence of any types to the type void
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* \see https://en.cppreference.com/w/cpp/types/void_t
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*/
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template <typename...>
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using void_t = void;
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/**
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* \brief To indicate that the contained object should be constructed in-place.
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* \see https://en.cppreference.com/w/cpp/utility/in_place
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*/
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#if defined(LIBIMP_CPP_17)
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using std::in_place_t;
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using std::in_place;
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#else /*!LIBIMP_CPP_17*/
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struct in_place_t {
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explicit in_place_t() = default;
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};
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constexpr in_place_t in_place {};
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#endif/*!LIBIMP_CPP_17*/
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/**
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* \brief A general pattern for supporting customisable functions
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* \see https://www.open-std.org/jtc1/sc22/WG21/docs/papers/2019/p1895r0.pdf
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*/
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namespace detail {
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void tag_invoke();
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struct tag_invoke_t {
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template <typename T, typename... A>
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constexpr auto operator()(T tag, A &&...args) const
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noexcept(noexcept(tag_invoke(std::forward<T>(tag), std::forward<A>(args)...)))
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-> decltype(tag_invoke(std::forward<T>(tag), std::forward<A>(args)...)) {
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return tag_invoke(std::forward<T>(tag), std::forward<A>(args)...);
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}
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};
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} // namespace detail
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constexpr detail::tag_invoke_t tag_invoke {};
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/**
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* \brief Circumventing forwarding reference may override copy and move constructs.
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* \see https://mpark.github.io/programming/2014/06/07/beware-of-perfect-forwarding-constructors/
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*/
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namespace detail {
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template <typename T, typename... A>
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struct is_same_first : std::false_type {};
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template <typename T>
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struct is_same_first<T, T> : std::true_type {};
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} // namespace detail
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template <typename T, typename... A>
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using is_not_match =
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typename std::enable_if<!detail::is_same_first<T,
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typename std::decay<A>::type...>::value>::type;
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LIBIMP_NAMESPACE_END_
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