From: "David A. Black" <dblack@...>
Date: 2009-09-09T20:17:05+09:00
Subject: Re: How to get the return value from method of the super class?

Hi --

On Wed, 9 Sep 2009, Josef Wolf wrote:

> Hello,
>
> I am trying to override a method of a superclass within my derived class.
> To do the real work, I need to call the original method of the superclass.
> But when I try to get the return value of the super method, I only get
> the object, not the return values I expected.  Here's a code snippet to
> demonstrate the problem, stripped from everything not related to the
> problem:
>
> jw@raven> cat ./test.rb
> #! /usr/bin/ruby
>
> require 'tk'
> require 'pp'
>
> root = TkRoot.new { title "pcb.rb" }
>
> class TkDerivedCanvas < TkCanvas
>  def coords(tag, *args)
>    super(tag, args)
>  end
> end
>
> orig    = TkCanvas.new(:scrollregion=>[0,0,500,400]).pack()
> derived = TkDerivedCanvas.new(:scrollregion=>[0,0,500,400]).pack()
>
> origrect    = TkcRectangle.new(orig,    [100,100], [300, 200], :fill=>"red")
> derivedrect = TkcRectangle.new(derived, [100,100], [300, 200], :fill=>"red")
>
> pp orig.coords(origrect)
> pp derived.coords(derivedrect)
>
> jw@raven> ./test.rb
> [100.0, 100.0, 300.0, 200.0]
> #<TkDerivedCanvas:0xb7cce11c @path=".w00001">
> jw@raven>
>
>
> Any ideas what I am doing wrong here?

Yes; the syntax of your call to super is wrong. If you want to call
super with the same arguments as the ones you got, just do:

   super

with no argument list. Also, in general, if you want to call another
method with the same arguments, you need to do:

   def m(*args)
     other(*args)   # note the *
   end

If you leave the * off of the call to other, you'll be sending a
single argument (an array) instead of a list of arguments (the
elements of the array).

In the case of super you don't need to do that; just don't provide any
argument list at all. (That's because super is a keyword, not a
method, and has its own semantics.)


David

-- 
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
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