Question

对于固定数量的模板参数，虽然手动编写的检查数量呈二次方增长，但这很容易。

#include <type_traits>

template <
    typename T1,
    typename T2,
    typename T3,
    typename T4>
struct unique_types
{
    static_assert(!std::is_same<T1, T2>::value, "Types must be unique");
    static_assert(!std::is_same<T1, T3>::value, "Types must be unique");
    static_assert(!std::is_same<T1, T4>::value, "Types must be unique");
    static_assert(!std::is_same<T2, T3>::value, "Types must be unique");
    static_assert(!std::is_same<T2, T4>::value, "Types must be unique");
    static_assert(!std::is_same<T3, T4>::value, "Types must be unique");
};

int main()
{
    // OK.
    unique_types<int, double, char, float> foo;

    // Should not compile.
    unique_types<int, double, char, double> bar;
}

如何为具有任意数量类型的参数包实现这一点？

Answer 1

你可以这样做：

#include <type_traits>

template <class ... Trest>
struct unique_types;

template <class T1, class T2, class ... Trest>
struct unique_types<T1, T2, Trest ...>
 : unique_types<T1, T2>, unique_types<T1, Trest ...>, unique_types<T2, Trest ...> {};

template <class T1, class T2>
struct unique_types<T1, T2>
{
    static_assert(!std::is_same<T1, T2>::value, "Types must be unique");
};

int main()
{
    // OK.
    unique_types<int, double, char, float> foo;

    // Should not compile.
    unique_types<int, double, char, double> bar;
}

如何检查参数包中的每个类型是否唯一？

1 个答案: