From: Richard Dale <Richard_Dale@...>
Date: 2003-07-15T05:12:21+09:00
Subject: Re: Custom method_missing doesn't trap super call

Yukihiro Matsumoto wrote:

> Hi,
> 
> In message "Custom method_missing doesn't trap super call"
>     on 03/07/15, Richard Dale <Richard_Dale@tipitina.demon.co.uk> writes:
> 
> |The non existent call to 't.baz()' is trapped ok. But in MyClass.foobar()
> |the 'super' call gives a 'no superclass method' error rather than calling
> |Base.method_missing as I expected. Does anyone know if there a way of
> |trapping the super call?
> 
> I feel like it's a bad idea in general, but without any particular
> reason.  Let me think.
Perhaps I should explain more what about I was trying to do - I didn't want
to over complicate the problem description. I'm working on bindings to a
C++ gui library Qt, and use a C method_missing (in the C 'Qt' extension) to
forward the calls to the C++ methods from ruby. When virtual methods are
overriden in ruby, like QPushButton::paintEvent(), it uses rb_respond_to()
to see whether or not there is a ruby version of the method.

if (rb_respond_to(obj, rb_intern(methodName)) == 0) {
        return false;
}
....
Otherwise if rb_respond_to() returns true, call ruby methods like
'paintEvent' below via rb_funcall2()

Then the call to 'super' needs to correctly invoke the C++ paintEvent()
method via the method_missing trap.
 

require 'Qt';

class MyClass < Qt::PushButton
        def paintEvent(event)
                printf("In paintEvent...\n")
                super
        end
end

a = Qt::Application.new(ARGV, ref nil);
hello = MyClass.new("Hello World", nil)
hello.resize(100, 30)
a.setMainWidget(hello)
hello.show()
a.exec()

> |Thanks for any help - I've just started with ruby - the syntax is really
> |nice and 'tidy' (ie un-C++ like :) ) The only other thing I got stuck
> |with is how to remove an item from a hash via C.
> 
> Use rb_hash_delete(hash, key);
Ah.. thanks thats ideal - I couldn't find it in intern.h with the other
rb_hash functions, so I assumed it didn't exist.

-- Richard