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From: adam.betts155@gmail.com
Newsgroups: comp.lang.ada
Subject: Re: Anonymous access types
Date: Fri, 08 Jun 2007 05:09:59 -0700
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Date: 2007-06-08T05:09:59-07:00
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On Jun 8, 1:01 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Fri, 08 Jun 2007 02:29:48 -0700, adam.betts...@gmail.com wrote:
> > I am having some trouble with anonymous access types, behaviour which
> > I do not understand. I have 2 questions:
>
> > 1) This one is bizarre and quite non-deterministic. I *sometimes* get
> > a "finalize/adjust raised exception" with the following bit of code:
>
> > declare
> >       t_ptr : tree_pointer := new tree'(get_tree(g));
> >       anon_t_ptr : access tree'class := new tree'(get_tree(g));
> >       lca : least_common_ancestor(anon_t_ptr);
> > begin
> > end;
>
> This leaks, where these objects get deallocated?

It was a deallocation problem, thanks

>
> > with the following type declarations:
> >  tree_pointer is access tree'class;
> >  type least_common_ancestor (tree_ptr: access constant tree'class);
>
> > It seems that there is sometimes a problem with the lca declaration,
> > since the exception is never raised when anon_t_ptr is replaced with
> > t_ptr.
>
> I guess it is because of accessibility checks. t_ptr and anon_t_ptr have
> different accessibility levels. When you call to least_common_ancestor,
> which probably has its parameter of some access type declared in an
> enclosing scope, then anon_t_ptr being converted fails on accessibility
> check. In the result you get a snowball of misleading secondary faults.
>
> (never use pointers if you can)
>
> > 2) I want to return an anonymous access type from a function:
>
> > function get_tree (g: graph) return non null access tree is
> > begin
> >   return new tree(g.t);
> > end get_tree;
>
> > The access type is not null when I use this function. However, when I
> > run the code and try to do operations on the access type, it is not
> > pointing in the right place. For example, the returned tree does not
> > have vertices and edges even though I know it does.
>
>    new tree(g.t);
>
> does not initialize the object beyond standard initialization. You probably
> meant
>
>    new tree'(<some initial value>);
>

Yep, sorry, was that a typo on my part. I actually did have:
      new tree'(g.t);
and not:
      new tree(g.t);

Given that, why does the pointer not point to the correct place? Where
is it pointing to since it is clearly not null and must be pointing to
a variable of type tree?