How to call a class member function from 2 void pointers

Question

So for this function:

template<typename T>
T popObject(ScriptObject obj) { //Preforms a cast from void* on each to its type.
    assert(obj.getType() == std::type_index(typeid(T))); //Ensure type Safety.
    return obj.get<T>();
}

template <typename C, typename...Args>
    void bind(const char* name, C* context, void(C::* function)(Args...)) {
        std::vector<std::type_index> arguments = { std::type_index(typeid(Args))... };
        auto functor = [](void* func,void* contex, std::vector<ScriptObject> stack) {
            std::size_t idx = 0;
            //Call class context -> function (Args...)
        };
        _functions[name] = new BoundFunction(functor, void_cast(function), context, arguments);
    }

I'm unsure of the syntax for calling the member function.

Iv tried:

union MF{
    void(C::* pf)(Args...);
    void* p;
} mf;
mf.p = func;
contex->*(mf.pf)(popObject<Args>(stack[idx++])...);

Which does not compile, Stating: "Does not evaluate to a function taking 1 Arguments."

Tried std::invoke, But I Don't know how to Specify the Member function Signature for arg1.

So If i have a reference to the member function, And a reference to the instance of the class, As well as the template information to Derive type information. How do I call the Classes member function?

Shot in the dark, still looking it over, have you tried popObject<Args...>? Or changing static_cast<C*>(contex).* to static_cast<C*>(contex)->? Also why are you casting pf to a type it already is? — The Floating Brain
(context->*(mf.pf))(...). First, it's ->* not .*, since you have a pointer on the left. Second, note the parentheses around context->*(mf.pf) part. — Igor Tandetnik
@TheFloatingBrain Thats a no go, Args... Would evaluate to template with each of the arguments, I still Want popObject to run on each Individual Argument. And -> only works if the member function name is known. — Steven Venham
@StevenVenham Sorry misread, but you should take a look at Igor's comment. Also if your function pointer pf takes in Args... does popObject return the type it gets from unfolding the pack? — The Floating Brain
Ok So changed to static_cast<C*>(ctx)->*(mf.pf)(popObject<Args>(stack[idx++])...); Good call on the extra static cast @TheFloatingBrain And Iv changed it to ->* Igor — Steven Venham

Steven Venham Steven Venham · Accepted Answer · 2020-05-26T00:49:36

Thanks @Igor Tandentnik

Final Solution was:

(static_cast<C*>(ctx)->*(mf.pf))(popObject<Args>(stack[idx++])...);

As Igor pointed out, it needed to be ->* instead of .*, and added parenthesis, as -> has a lower priority then the Function call operator.

Also, thanks @TheFloatingBrain for pointing out the extra static_cast

How to call a class member function from 2 void pointers

1 Answers