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败犬日报 2025-02-03 ​

1. 函数限定类型 ​

来自 proxy 库的代码：

cpp
template <class R, class... Args>
struct overload_traits<R(Args...)>
    : overload_traits_impl<qualifier_type::lv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) noexcept>
    : overload_traits_impl<qualifier_type::lv, true, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) &>
    : overload_traits_impl<qualifier_type::lv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) & noexcept>
    : overload_traits_impl<qualifier_type::lv, true, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) &&>
    : overload_traits_impl<qualifier_type::rv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) && noexcept>
    : overload_traits_impl<qualifier_type::rv, true, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const>
    : overload_traits_impl<qualifier_type::const_lv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const noexcept>
    : overload_traits_impl<qualifier_type::const_lv, true, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const&>
    : overload_traits_impl<qualifier_type::const_lv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const& noexcept>
    : overload_traits_impl<qualifier_type::const_lv, true, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const&&>
    : overload_traits_impl<qualifier_type::const_rv, false, R, Args...> {};
template <class R, class... Args>
struct overload_traits<R(Args...) const&& noexcept>
    : overload_traits_impl<qualifier_type::const_rv, true, R, Args...> {};

函数的限定类型只能枚举，没有简化的写法。

完整一共 48 种情况，即下面的几个排列组合 3 × 2 × 2 × 2 × 2：

  • 无引用、引用、右值引用
  • 是否 const
  • 是否 volatile
  • 是否 noexcept
  • 是否 variadic（C 风格的变参）