C ++ 11静态断言是否等于可比较类型？ [英] C++11 static assert for equality comparable type?

问题描述

在C ++ 11中，如何使用EqualityComparable概念来模板类型为 static_assert ？

How to static_assert a template type is EqualityComparable concept in C++11?

推荐答案

您可以使用以下类型特征：

You could use the following type trait:

#include <type_traits>

template<typename T, typename = void>
struct is_equality_comparable : std::false_type
{ };

template<typename T>
struct is_equality_comparable<T,
    typename std::enable_if<
        true, 
        decltype(std::declval<T&>() == std::declval<T&>(), (void)0)
        >::type
    > : std::true_type
{
};

您将以这种方式进行测试：

Which you would test this way:

struct X { };
struct Y { };

bool operator == (X const&, X const&) { return true; }

int main()
{
    static_assert(is_equality_comparable<int>::value, "!"); // Does not fire
    static_assert(is_equality_comparable<X>::value, "!"); // Does not fire
    static_assert(is_equality_comparable<Y>::value, "!"); // Fires!
}

这是 实时示例 。

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