Question

In c++ it is allowed to create a template on functions, both member and free

template <void (*F) ()> void function1 ();
template <void (MyClass::*M) ()> void function2 ();

and instantiate them explicitly

function1 <&fn> ();
function2 <&MyClass::doSomething> ();

my question is, if the template arguments themselves are instantiated from templates

template <typename R, typename C, R (C::*M) ()> void function3 ();

how do I instantiate function3 explicitly (if even possible)?

Answer 1

Just do:

function3<void, MyClass, &MyClass::doSomething>();

The syntax is just the same in this case as in the other cases.

Complete compilable example:

#include <iostream>
class MyClass {
public:
    void doSomething() {
        std::cout << "doSomething\n";
    }
};
void fn() {
    std::cout << "fn\n";
}
template <void (*F) ()> void function1 () {
    F();
}
template <void (MyClass::*M) ()> void function2 () {
    (MyClass().*M)();
}
template <typename R, typename C, R (C::*M) ()> void function3 () {
    (C().*M)();
}
int main() {
    function1<&fn>();
    function2<&MyClass::doSomething>();
    function3<void, MyClass, &MyClass::doSomething>();
}

Prints:

fn
doSomething
doSomething