How to template a function to take arbitrary functions or methods as parameter

Question

I'd like to write a function which can both take a function or a method as parameter. ie a function accepting the same parameter than the std::thread constructor.

So far I have something working for a function but have hard time for methods:

template<typename F, typename... Args>
typename std::result_of<typename std::decay<F>::type(typename std::decay<Args>::type...)>::type
call(F &&func, Args... args) {
    return func(args...);
}

void hello() { std::cout << "hello\n"; }

class Hello {
public:
    Hello() = default;
    ~Hello() = default;
    void hello() { std::cout << "hello\n"; }
};

int main()
{
    // func
    call(hello);

    // meth
    Hello h;
    call(&Hello::hello, &h);
}

I tried to reproduce what is done by the contructor of std::thread but struggle to find the right way to write it.

You could just wrap any methods into a lambda expression instead. It might be much easier. — Tomáš Zato, May 10 '21 at 12:34
You want to look up std::invoke. If you cannot use it, you probably need to write an overload for member function pointers. — n. m. could be an AI, May 10 '21 at 12:35
@n. 'pronouns' m. Yes i saw https://en.cppreference.com/w/cpp/utility/functional/invoke but i'm stuck to c++14. How would you write an overload for member function pointers ? It's basically what i fail to do '^^ — René paul Debroize, May 10 '21 at 12:39
Basically what you want is [`std::invoke`](https://en.cppreference.com/w/cpp/utility/functional/invoke), but that requires C++17. — NathanOliver, May 10 '21 at 12:39
template auto call(F &&func, Args&&... args) -> decltype(std::ref(func)(std::forward(args)...)) { return std::ref(func)(std::forward(args)...); } do the trick for it worth. — René paul Debroize, May 10 '21 at 13:09
You can try and copy a possible implementation from here https://en.cppreference.com/w/cpp/utility/functional/invoke — n. m. could be an AI, May 10 '21 at 13:55

How to template a function to take arbitrary functions or methods as parameter

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