How to Check if a Template Class has the Given Member Function in C++?

// C++ program to check whether a templated class has a
// member function or not.

#include <iostream>
using namespace std;

// Define a template class 'temp'
template <typename T> class temp {
public:
    // Member function 'func' that returns a bool
    bool func(const T& element) { return true; }
};

// Define a template class 'check' to test for the existence
// of 'func'
template <typename T> class check {
    // Define two types of character arrays, 'yes' and 'no',
    // for SFINAE test
    typedef char yes[1];
    typedef char no[2];

    // Test if class T has a member function named 'func'
    // If T has 'func', this version of test() is chosen
    template <typename C>
    static yes& test(decltype(&C::func));

    // Fallback test() function used if T does not have
    // 'func'
    template <typename> static no& test(...);

public:
    // Static constant 'value' becomes true if T has 'func',
    // false otherwise The comparison is based on the size
    // of the return type from test()
    static const bool value
        = sizeof(test<T>(0)) == sizeof(yes);
};

int main()
{
    // Test if 'temp<int>' has a member function 'func'
    cout << boolalpha << check<temp<int> >::value
         << endl; // Outputs true

    // Test if 'temp<double>' has a member function 'func'
    cout << boolalpha << check<temp<double> >::value
         << endl; // Outputs true

    return 0;
}