Hi

I am trying to register a class member function as wc.lpfnWndProc, but get the error message "cannot implicitly convert expression (&this.WndProc) of type extern (Windows) int delegate(...) to extern (Windows) int function(...).

I have:

extern (Windows)
class App
{
    HRESULT initialize(HINSTANCE hInstance, int iCmdShow)
    {
        WNDCLASS wc;
        ...
        wc.lpfnWndProc = &wndProc;
        ...
    }

    HRESULT wndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
    {
        switch (message)
        {
            ...
        }
    }
    ...
}


(Defining wndProc as a global function works, but is not what I want to do...)
What is the issue here and how do I make it work?

On Friday, 28 September 2012 at 17:53:59 UTC, deed wrote:

> (Defining wndProc as a global function works, but is not what I want to do...)
> What is the issue here and how do I make it work?

You are interfacing with C, which does not support functions with state (delegate). You must pass it a function, and while you can get at the function pointer of a delegate this is unsafe.

You make it work by providing a function and not a delegate. I do not know how to wrap a delegate to make that work.

On Friday, 28 September 2012 at 17:53:59 UTC, deed wrote:
> Hi
>
> I am trying to register a class member function as wc.lpfnWndProc, but get the error message "cannot implicitly convert expression (&this.WndProc) of type extern (Windows) int delegate(...) to extern (Windows) int function(...).
>
> I have:
>
> extern (Windows)
> class App
> {
>     HRESULT initialize(HINSTANCE hInstance, int iCmdShow)
>     {
>         WNDCLASS wc;
>         ...
>         wc.lpfnWndProc = &wndProc;
>         ...
>     }
>
>     HRESULT wndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
>     {
>         switch (message)
>         {
>             ...
>         }
>     }
>     ...
> }
>
>
> (Defining wndProc as a global function works, but is not what I want to do...)
> What is the issue here and how do I make it work?

Because wndProc in your case cannot be converted to a delegate. You can make it a module-level function (there is no globals in D) or try to make it static function - I currently cannot check whether it works. In any way, what gives you making wndProc a class member function?

On 9/28/12, Maxim Fomin <maxim@maxim-fomin.ru> wrote:
> try to make it static function

If only one app is ever supposed to be instantiated you can use a static function and a static reference to the class instance: http://dpaste.dzfl.pl/b1497fa1

Otherwise you could use a hashmap to redirect wndProc's to class instances by using a HWND as the key and App as the value, something like:

App[HWND] apps;

extern (Windows)
LRESULT winDispatch(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    auto app = hwnd in apps;

    if (app !is null)
    {
        return app.wndProc(hwnd, message, wParam, lParam);
    }

    return DefWindowProc(hwnd, message, wParam, lParam);
}

apps would be written to any time a new App instance is created.
Anyway there are multiple ways of doing this, it depends on what you need.

Thanks to all of you for your informative replies. I was testing different code structures and wondered whether this was possible.