探测模板参数

#include <iomanip>
#include <iostream>
#include <map>
#include <type_traits>
#include <vector>

// 探测成员
#define DEFINE_HAS_MEMBER(Member)                                                     \
    template <typename, typename = std::void_t<>>                                     \
    struct HasMemberT_##Member                                                        \
        : std::false_type                                                             \
    {                                                                                 \
    };                                                                                \
    template <typename T>                                                             \
    struct HasMemberT_##Member<T, std::void_t<decltype(&T::Member)>> : std::true_type \
    {                                                                                 \
    };
DEFINE_HAS_MEMBER(size);

void Test()
{
    std::cout << HasMemberT_size<int>::value << std::endl;              // 0
    std::cout << HasMemberT_size<std::vector<int>>::value << std::endl; // 1
}

// 萃取类型是否包含成员方法
template <typename, typename = std::void_t<>>
struct IsBeginT : std::false_type
{
};

template <typename T>
struct IsBeginT<T, std::void_t<decltype(std::declval<T>().begin())>> : std::true_type
{
};

void Test1()
{
    std::cout << IsBeginT<char>::value << std::endl;
    std::cout << IsBeginT<std::vector<int>>::value << std::endl;
}

int main()
{
    Test1();
}