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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Use of declare blocks
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Date: Thu, 22 Mar 2007 09:34:20 +0100
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Date: 2007-03-22T09:34:20+01:00
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On Wed, 21 Mar 2007 22:43:58 +0200, Niklas Holsti wrote:

> Randy Brukardt wrote:
> 
>> I use declare blocks extensively to reduce the scope of temporary variables
>> in subprograms. They're especially important when the object exists just to
>> take an unused out parameter, because they greatly reduce the need to come
>> up with names for the objects. I often have code like:
>> 
>>     declare
>>             Junk : Index;
>>     begin
>>             Insert_Something (..., Result => Junk);
>>     end;
>> 
>> where the result isn't needed by the following code.
> 
> How about a language extension to omit unused out parameters, for example
> 
>     Insert_Something (..., Result => <>);

Unused function results are even more offending. I would like to see:

   null <expression>;

instead of

   declare
      Dummy : Guess_What;
   begin
      Dummy := <expression>;
   end;

> Perhaps even allowing declaration of optional out parameters, as in
> 
>     procedure Insert_Something (..., Result : out Index := <>);
>
> and then a call of Insert_Something could omit Result entirely.

That could be difficult because of discriminants. Consider:

   procedure Insert_Something (..., Result : in out String (1..80) := <>);
   procedure Insert_Something (..., Result : in out String (<>) := <>);
  ...

I guess if optional [in] out parameters weren't better solvable with lazy
expressions. If the latter were supported one could provide a non-intrusive
default for outs without magical stuff like <>.

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