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From: Justin Gombos <rpbkbq.xax.gld@uluv.kbq>
Subject: Re: private types
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Date: Fri, 17 Mar 2006 22:50:30 GMT
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Date: 2006-03-17T22:50:30+00:00
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On 2006-03-17, Brian May <bam@snoopy.apana.org.au> wrote:
> I am not sure how this:
>
>   function exists return boolean is
>
>     --Later assignment to found_it is evitable
>     --
>     found_it : boolean := false; 
> 
>   begin
>
>     if some_precondition then
>
>       found_it := some_other_condition;
>
>     end if;
>
>     return found_it;
>
>   end exists;
>
> Is any better/worse then this:
>
>   function exists return boolean is
>
>     --Later assignment to found_it is evitable
>     --
>     found_it : boolean;
>
>   begin
>
>     if some_precondition then
>
>       found_it := some_other_condition;
>
>     end if;
>
>     return found_it;
>
>   end exists;

The second case is obviously careless, and as you say, unpredictible.
The first case is a good approach, as is this alternative:

  function exists return boolean is

    --Later assignment to found_it is inevitable
    --
    found_it : boolean;

  begin

    if some_precondition then

      found_it := some_other_condition;
  
    else

      found_it := a_different_condition;

    end if;

    return found_it;

  end exists;
 
My main purpose was to put the spotlight on this foolish practice:

  function exists return boolean is

    --Later assignment to found_it is inevitable
    --
    found_it : boolean := false; --needless and misleading initialization

  begin

    if some_precondition then

      found_it := some_other_condition;
  
    else

      found_it := a_different_condition;

    end if;

    return found_it;

  end exists;

Users of the OPs API might be forced into this scenario if the API is
constructed to force explicit initialization on instantiation.

> It is possible a smart compiler might trigger a warning in the
> second case - but this depends on you noticing the warning and
> investigating it. There are cases when the compiler might get
> confused and produce false positives or false negatives.
>
> Otherwise, the above problem is a problem that can only be found
> either by careful inspection of the code or by proper testing.

Sure there are multiple opportunities to find flaws; but the idea is
to not depend on them more than we have to.

-- 
PM instructions: do a C4esar Ciph3r on my address; retain punctuation.