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Newsgroups: comp.lang.ada
Subject: Re: Access to function returning class-wide type
Date: Thu, 21 Aug 2008 13:56:35 +0200
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Date: 2008-08-21T13:56:35+02:00
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Dmitry A. Kazakov wrote:

>> What I need is a access type to 'constructor' of an derivate of abstract
>> object.
>> As I presented, there is a workaround, but that's not the 'right' way to
>> do it. I really want to do it without some tricky wrapping.
>> How do I define The_Access_Type to do what I want?
> See Ada.Tags.Generic_Dispatching_Constructor. It gives you a function
> constructing an object from the type tag, the parameters (Natural in your
> case) using the function you want (Proc). It goes as follows:
> 
> with Ada.Tags.Generic_Dispatching_Constructor;
> package A is
>    type Abstracted is abstract tagged null record;
>    function Proc (N : not null access Natural)
>       return Abstracted is abstract;
>    function Constructor is
>       new Ada.Tags.Generic_Dispatching_Constructor
>              (Abstracted, Natural, Proc);
> end A;

I belive that would work too, but at the cost of defining function Proc (N :
not null access Natural) return ... for each descendant type. That would be
another wrapper, so it's the same resolution to the problem as Proc_Wrapper
in my original code, assuming that I need Proc (N : Natural) as well.

Tell me that I'm wrong, please ;-)

-- 
Paweł Płazieński aka Nivertius
"In the end, there will be Ada, XML and gzip"