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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: another way to shoot yourself in the foot?
Newsgroups: comp.lang.ada
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Date: Mon, 23 Jun 2008 09:49:26 +0200
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Date: 2008-06-23T09:49:26+02:00
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On Sun, 22 Jun 2008 16:44:08 -0400, Robert A Duff wrote:

> I don't see that as a problem, and anyway, the same thing can happen
> with the existing syntax:
> 
> function Foo (...) return String is
> begin
>    return Result : String (1..200) do  -- Going to return 200 characters
>       Result (1) := 'a'; -- Here the result has to be allocated
>       if HALT (x) then
>          goto Label;
>       end if;
>    end;  -- Drop already allocated and initialized result
>    <<Label>>
>    return "Hallo!";  -- Return a completely different thing
> end Foo;
> 
> The implementation of this is "interesting" (if we replace String by a
> build-in-place type).  ;-)

How much interesting is it? (:-))

Unfortunately the following crazy sample crashes GNAT, but I wonder what
could be the result if it compiled:

procedure Return_Task is
   Just_For_Fun : exception;

   task type T is
      entry A;
   end T;

   task body T is
   begin
      accept A;
   end T;

   function Interesting return T is
   begin
      return X : T do
         raise Just_For_Fun;
      end return;
   exception
      when Just_For_Fun =>
         return X : T;
   end Interesting;

   X : T := Interesting;
begin
   X.A;
end Return_Task;

Should it block?

Another question is about the semantics such stuff. In which sense in-place
is it? It seems that an in-place initialization might result in n
finalizations and n+1 initializations (n>=0) of the same thing.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de