c++ type trait 之 类型判断工具

//type trait 之类型判断工具#include <iostream>#include <array>using namespace std;enum class color{    red,green,blue};auto f = [](){    cout << "I'm lambda" << endl;};union A{    int a;    float b;    string c;};class B{public:    int b;    void f() {}};int main(){    //is void?    cout << boolalpha << is_void<void>::value << endl;    //整数类型包括(bool char int char16_t char32_t wchar_t)?    cout << boolalpha << is_integral<int>::value << endl;    //浮点数(float double long double)?    cout << boolalpha << is_floating_point<int>::value << endl;    //算术类型(包括整数和浮点数)？arithmetic    cout << boolalpha << is_arithmetic<string>::value << endl;    //带正负号的arithmetic type    cout << boolalpha << is_signed<string>::value << endl;    //不带正负号的arithmetic type    cout << boolalpha << is_unsigned<int>::value << endl;    //对象是否带有const限定符    cout << boolalpha << is_const<const int*>::value << endl;    //对象是否带有volatile限定符    cout << boolalpha << is_volatile<volatile int * volatile>::value << endl;    //row array ?    cout << boolalpha << is_array<array<int,5>>::value << endl;    // enum ?    cout << boolalpha << is_enum<color>::value << endl;    // union ?    cout << boolalpha << is_union<A>::value << endl;    // class(class or struct but nou union) ?    cout << boolalpha << is_class<A>::value << endl;    //function type?    cout << boolalpha << is_function<decltype(f)()>::value << endl;    // reference ?    cout << boolalpha << is_reference<int&&>::value << endl;    // left reference ?    cout << boolalpha << is_lvalue_reference<int&&>::value << endl;    // right reference ?    cout << boolalpha << is_rvalue_reference<int&&>::value << endl;    // row pointer ?    cout << is_pointer<int*>::value << endl;    //pointer to nonstatic 成员 ?    cout << is_member_pointer<decltype(&B::f)>::value << endl;    //pointer to nonstatic 数据成员    cout << is_member_object_pointer<decltype(&B::f)>::value << endl;    //pointer to nonstatic 成员函数    cout << is_member_function_pointer<decltype(&B::f)>::value << endl;    //包括(整型,void,浮点型,std::nullptr_t)    cout << is_fundamental<string>::value << endl;    //整型 浮点数 枚举(enumeration) pointer,member pointer,std::nullptr_t    cout << is_scalar<int>::value << endl;    //任何类型除void reference pointer function array enumeration union     //class     cout << is_object<string>::value << endl;    system("pause");    return 0;}