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From: "Alex R. Mosteo" <alejandro@mosteo.invalid>
Newsgroups: comp.lang.ada
Subject: Re: ANN: Ada industrial control widget library v1.0 released
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Date: Thu, 17 Feb 2011 14:02:03 +0100
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Dmitry A. Kazakov wrote:

> On Wed, 16 Feb 2011 11:45:13 +0100, Alex R. Mosteo wrote:
> 
>> (snip)
> 
> I tried a bit by defining interfaces of drawable layers. I intentionally
> didn't make layer a GObject for this reason. But that was the easy part.
> 
>> And I wonder how/if many access types would be needed.
> 
> Lots, because GUI objects involved do not have their life times bound to a
> static scope. Objects are created and put into some container (e.g.
> widget) of class-wide instances. Ada cannot this without access types for
> many reasons. Similarly when an object is referenced, you need to be able
> to return it by-reference from a getter/setter function. By-reference
> result was ditched in Ada 2005 in favor of meaningless and useless
> limited-valued functions. There are other issues too, like dispatching on
> bare tags (generic dispatching constructor does not really work),
> immutable results (that is when you reference a limited element of an
> immutable container, the subtype of the result must be immutable. But when
> the container is mutable, the result is mutable too. C++ solves it by
> overloading, but I don't like that.)

Thanks, this is the kind of stuff that goes over my head, and where I can 
really use other's knowledge. Instructive, even if it the subject is purely 
hypothetical at this time.

Alex.

> I think it is possible to get rid of access types in GUI, if ARG
> considered this as a goal and changed the language accordingly. Nowhere in
> GUI objects are referenced without their containers and there is always a
> dedicate owner of each object.