Judge whether the two types are the same

There is one in the standard library std::is_same Class template for , Used to judge whether the two types are the same , Take a look at the following test first :

int main()
{
    
	cout << std::is_same<int, int>::value << endl;
	cout << std::is_same<int, double>::value << endl;
	cout << std::is_same<int, const int>::value << endl;
	system("pause");
	return 0;
}

result ;

How to realize one by yourself ？

template<typename T1, typename T2>
struct IsSameType
{
    
	static const int value = 0;
};

template<typename T1>
struct IsSameType<T1,T1>
{
    
	static const int value = 1;
};


int main()
{
    
	cout << IsSameType<int, int>::value << endl;
	cout << IsSameType<int, double>::value << endl;
	cout << IsSameType<int, const int>::value << endl;
	system("pause");
	return 0;
}

result ：

You can use a variable template to make an improvement .
Be careful ： Cannot use alias template , Because the result is a value , Not a type .

template<typename T1,typename T2>
const int IsSame_v = IsSameType<T1, T2>::value;

int main()
{
    
	cout << IsSame_v<int, int> << endl;
	cout << IsSame_v<int, double><< endl;
	cout << IsSame_v<int, const int><< endl;
	system("pause");
	return 0;
}

result ：

In fact, you can also optimize class templates , as follows ：

template<typename T1, typename T2>
struct IsSameType:false_type
{
    
};

template<typename T1>
struct IsSameType<T1,T1>:true_type
{
    
};

template<typename T1,typename T2>
const int IsSame_v = IsSameType<T1, T2>::value;

int main()
{
    
	cout << IsSame_v<int, int> << endl;
	cout << IsSame_v<int, double><< endl;
	cout << IsSame_v<int, const int><< endl;
	system("pause");
	return 0;
}

result ：