You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
70 lines
2.5 KiB
70 lines
2.5 KiB
// -----------------------------------------------------------------------------
|
|
// Detection idiom adapted from "Working Draft, C++ Extensions for Library Fundamentals, Version 3":
|
|
// https://cplusplus.github.io/fundamentals-ts/v3.html#meta.detect
|
|
// -----------------------------------------------------------------------------
|
|
|
|
#pragma once
|
|
|
|
#include <type_traits>
|
|
|
|
// In case we do support c++17 just use the headers shipped with the GCC
|
|
#if __cplusplus >= 201703L
|
|
#include <type_traits>
|
|
#include <experimental/type_traits>
|
|
using std::experimental::is_detected;
|
|
#else
|
|
|
|
namespace experimental_type_traits {
|
|
namespace implementation {
|
|
// Small workaround for GCC-4.8.2 to *really* trigger substitution error with void_t
|
|
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64395
|
|
// https://stackoverflow.com/a/35754473
|
|
template <typename... >
|
|
struct make_void {
|
|
using type = void;
|
|
};
|
|
|
|
template <typename... T>
|
|
using void_t = typename make_void<T...>::type;
|
|
|
|
// Return dummy type as the Default type
|
|
struct nonesuch {
|
|
nonesuch() = delete;
|
|
~nonesuch() = delete;
|
|
nonesuch(nonesuch const&) = delete;
|
|
void operator=(nonesuch const&) = delete;
|
|
};
|
|
|
|
// Implementation of the detection idiom (negative case).
|
|
template<typename Default, typename AlwaysVoid,
|
|
template<typename...> class Op, typename... Args>
|
|
struct detector {
|
|
using value_t = std::false_type;
|
|
using type = Default;
|
|
};
|
|
|
|
// Implementation of the detection idiom (positive case).
|
|
template<typename Default, template<typename...> class Op,
|
|
typename... Args>
|
|
struct detector<Default, void_t<Op<Args...>>, Op, Args...> {
|
|
using value_t = std::true_type;
|
|
using type = Op<Args...>;
|
|
};
|
|
}
|
|
|
|
template<template<typename...> class Op, typename... Args>
|
|
using is_detected = typename implementation::detector<implementation::nonesuch, void, Op, Args...>::value_t;
|
|
|
|
template <template<class...> class Op, class... Args>
|
|
using detected_t = typename implementation::detector<implementation::nonesuch, void, Op, Args...>::type;
|
|
|
|
template <class Default, template<class...> class Op, class... Args>
|
|
using detected_or = implementation::detector<Default, void, Op, Args...>;
|
|
|
|
// ...
|
|
// implement the rest as needed. some things may not work though
|
|
}
|
|
|
|
using experimental_type_traits::is_detected;
|
|
|
|
#endif // __cplusplus >= 201703L
|