CODEWITHSUNDEEP
c++
Stew
Stew

Reputation: 11

Static templated member function as function pointer

I'm attempting to replace a series of static to non static member function pairs throughout my code, I can achieve this with a macro but I was hoping I could do so with a static function which takes the non static member function as a template argument, which then gets stored as a function pointer. See the following code:

struct widget_param
{
    void* ptr;
};

struct widget_data
{
    bool(*callback)(widget_param*);
};

template <class CLASSNAME>
class widget_base
{
protected:
    static CLASSNAME* get_instance(widget_param* param)
    {
        return static_cast<CLASSNAME*>(param->ptr);
    }

public:
    template <bool(CLASSNAME::*f)(widget_param*)>
    static bool static_to_nonstatic(widget_param* param)
    {
        return get_instance(param)->*f(param);
    }
};

class widget_derived : public widget_base<widget_derived>
{
public:
    // Attempting to replace this function
    static bool static_do_stuff(widget_param* param)
    {
        return get_instance(param)->do_stuff(param);
    }
    bool do_stuff(widget_param* param)
    {
        param;
        cout << "Success!";
        return true;
    }
};

int main() {
    widget_derived derived;
    //widget_data data{ widget_derived::static_do_stuff}; // Current approach
    widget_data data{ widget_derived::static_to_nonstatic<widget_derived::do_stuff> };

    widget_param param{ &derived };
    data.callback(&param);
    return 0;
}

I was expecting the template to evaluate to:

static bool static_to_nonstatic(widget_param* param);

Is it possible to do what I'm trying to achieve, without resorting to using a macro?

Upvotes: 0

Views: 60

Answers (1)

Stew
Stew

Reputation: 11

Resolved, since the call is to a member function pointer - it needed to be surrounded by parenthesis, changed the template to the following and it worked:

template <bool(CLASSNAME::*f)(widget_param*)>
static bool static_to_nonstatic(widget_param* param)
{
    return (get_instance(param)->*f)(param);
}

Upvotes: 1

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