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Date: Fri, 24 Oct 2008 15:24:50 +0300
From: Niklas Holsti <niklas.holsti@tidorum.invalid>
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Newsgroups: comp.lang.ada
Subject: Re: How to pass around access types to interfaces?
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Date: 2008-10-24T15:24:50+03:00
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Sven wrote:
> I'm learning Ada and I've run into a big problem with passing around
> access types to interfaces. I guess I just don't know all the
> subtleties of access types, I'm used to C/C++ pointers. I didn't find
> anything helpful on the net or in the  Ada Reference Manual.
> 
> I'm trying to get this code to run:
> 
> in some package:
>   type My_Interface is interface;
>   type My_Interface_Access is access all My_Interface'Class;
> 
>   procedure Do_Something( Item : in out Some_Object; With :
> My_Interface_Access );
> 
> in main program:
>   type Concrete_Type is new My_Interface with ...;

I assume this type declaration is in the main *procedure*. This 
means that the type has a local scope and life, which prevents 
converting its values to a more long-lived access type. Try 
declaring Concrete_Type in a package; that makes it live as long as 
the whole program, and should allow such conversions.

HTH,

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .