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Date: Thu, 27 Jan 2011 18:50:22 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Equivalent of dynamic_cast (downcast) for tagged types
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Date: 2011-01-27T18:50:22+01:00
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On 27.01.11 17:18, Dmitry A. Kazakov wrote:

> The above is a bad idea, because X might be a descendant of T which has
> overridden Do_Something. So you might be looking for this
> 
>    if X'Tag = T'Tag then -- X is of T
>       Do_Something (T (X));  -- No dispatch
>    end if;
> 

The following seems to be working in Pure units, too,
since it does not depend on Ada.Tags:

    procedure Foo (X : in out P.Some_Interface'Class) is
    begin
        declare
            Dynamic_Cast_X : Descendant.T renames Descendant.T(X);
        begin
            Dynamic_Cast_X.Do_Something_For_Me;
        end;
    exception
        when CE:  Constraint_Error =>
            -- X not of type Descendant.T ...
            null;
    end Foo;