From: Josef Wolf <jw@...>
Date: 2006-09-07T02:10:25+09:00
Subject: Re: How to store/load persistent data?

On Wed, Sep 06, 2006 at 07:17:46AM +0900, Timothy Hunter wrote:
> Josef Wolf wrote:
 
> There is a well-known Ruby idiom for coding block-scoped resources. 
> There used to be a good page describing this in RubyGarden but alas that 
> page seems to have disappeared. Anyway, here's the general example from 
> that page:
> 
> > def Resource.open( identifier )  # :yield: resource
> >     resource = Resource.new( identifier )
> >     if block_given?
> >         begin
> >             yield resource
> >         ensure
> >             resource.close
> >         end
> >     else
> >         return resource
> >     end
> > end
> 
> That is, create/open/whatever the resource is and yield to a block. 
> Within the block use the resource. When the block returns, close/destroy 
> the resource. The open method in the IO class is prototypical.

I am aware of this idiom.  This idiom works very well if you have a strictly
hierachical call structure.

But I just can't see how this can help when dealing with Tk (especially
with canvas items).  In this case, objects are created and destroyed
asynchronously.  The block that creates a new widget has to return
_before_ the widget is destroyed.

Of course, with widgets like TkDialog, this idiom would work very well
since dialog->Show() blocks until the widget is destroyed.  OTOH, TkDialog
don't need this idiom since it is already destroyed when its Show method
returns.