如何使用 SFINAE 检测 noexcept 方法 [英] How to detect a noexcept method using SFINAE

问题描述

我问的是一个(流行的)问题的变体 - 检测类的方法的存在.

I'm asking about a variation of a (popular) question - detecting the existence of a method of a class.

我在这里阅读了很多答案，大多数(C++17 后)解决方案看起来像 这个:

I've read many answers here in SO, and most of the (post C++17) solutions look like this:

#include <type_traits>

template<class ...Ts>
struct voider{
    using type = void;
};

template<class T, class = void>
struct has_foo : std::false_type{};

template<class T>
struct has_foo<T, typename voider<decltype(std::declval<T>().foo())>::type> : std::true_type{};

基本上，我们让编译器决定使用技巧":如果表达式 std::declval().foo() 是良构的，然后 decltype(std::declval<T>().foo()) 不会产生编译器错误，那么编译器更喜欢" has_foo<T, typename voider<decltype(...)>>::type 因为它不需要用默认类型替换第二个模板类型.

Basically, we're letting the compiler decide using a "trick" : if the expression std::declval<T>().foo() is well-formed, then decltype(std::declval<T>().foo()) doesn't produce a compiler-error, then the compiler "prefers" has_foo<T, typename voider<decltype(...)>>::type since it doesn't need to replace the second template type with a default type.

很好，但是我们如何将 noexcept 与它结合起来呢?我尝试了很多方法，但似乎大多数技术(包括 decltype(declval<type>.my_func()))只关心名称、返回类型和参数类型，而不关心 noexcept.

great, but how can we combine noexcept with it? I've tried many ways but it seems most techniques (including decltype(declval<type>.my_func())) only care about the name, return type and the argument types and not about the noexcept.

推荐答案

您可以在 noexpect 运算符(C++11 起).

You can do it with the help of noexpect operator (since C++11).

noexcept 运算符执行编译时检查，如果表达式声明为不抛出任何异常，则返回 true.

The noexcept operator performs a compile-time check that returns true if an expression is declared to not throw any exceptions.

例如

template<class T>
struct has_foo<T, 
               typename voider<decltype(std::declval<T>().foo()),
                               std::enable_if_t<noexcept(std::declval<T>().foo())>
                              >::type
              > : std::true_type{};

直播

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