Array of function pointers ( including member functions) throwing template specialization error

Question

So, I have a class called Delegate that can store an array of function pointers. This is the code:

template<typename Func>
class delegate
{
private:
public:
    typename std::vector<Func> mListOfFunctions;
    void Bind(Func f)
    {
        mListOfFunctions.push_back(f);
    }
    template<typename...TArgs>
    void Invoke(TArgs&&...arg)
    {
        for (auto f : mListOfFunctions)
        {
            f(std::forward<TArgs>(arg)...);
        }
    }
};

Usage in Player.cpp:

delegate<void(float)> testDelegate;
testDelegate.Bind(std::bind(&Player::MoveLeft,this));

This throws the error C2893 (Error C2893 Failed to specialize function template 'unknown-type std::invoke(_Callable &&,_Types &&...)')

But when I change the definition of Bind to the following:

template<typename F>    
void Bind(F f)
{

}

It works fine, but when I try to push the function object into the vector it throws the same error again.

Is there anyway to resolve this?

I need to cache the pointers passed in.

Answer 1

The result of std::bind is not a function pointer (it is a function object of an unspecified type), but you're trying to make it into one. Since you're using std::forward, you must be using C++11, which means you can use std::function:

template<typename Func>
class delegate
{
private:
public:
    typename std::vector<std::function<Func>> mListOfFunctions;
    void Bind(std::function<Func> f)
    {
        mListOfFunctions.push_back(f);
    }
    template<typename...TArgs>
    void Invoke(TArgs&&...arg)
    {
        for (auto f : mListOfFunctions)
        {
            f(std::forward<TArgs>(arg)...);
        }
    }
};