Re: Call method if declared only

[Simen Kjærås via Digitalmars-d-learn]

On Friday, 28 February 2020 at 09:25:58 UTC, Виталий Фадеев wrote:
Yes. Thank !
I read it.
Problem is - OS has many messages + user messages... It mean 
what interfaces like IKeyDown must me declared. All. Dream on 
write less code...

So let's create a template for that:

interface IMessageHandler(alias msg) {
    mixin("LRESULT On"~__traits(identifier, msg)~"(WPARAM wParam, 
LPARAM lParam);");
}

And use it:

import core.sys.windows.windows;
import std.stdio;

class Base {
    LRESULT On(UINT message, WPARAM wParam, LPARAM lParam) {
        switch (message) {
            case WM_KEYDOWN:
                if (auto that = 
cast(IMessageHandler!WM_KEYDOWN)this) {
                    return that.OnWM_KEYDOWN(wParam, lParam);
                }
                break;
            default:
        }
        return 0;
    }
}

class Button : Base, IMessageHandler!WM_KEYDOWN {
    LRESULT OnWM_KEYDOWN(WPARAM wParam, LPARAM lParam) {
        writeln("WM_KEYDOWN");
        return 0;
    }
}

unittest {
    Base b1 = new Base();
    Base b2 = new Button();

    writeln("Base:");
    b1.On(WM_KEYDOWN, 0, 0);
    writeln("Button:");
    b2.On(WM_KEYDOWN, 0, 0);
}

You'll still have to specify for each derived class which 
messages they handle, but no need to define hundreds of 
interfaces separately.

--
  Simen