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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Use of declare blocks
Date: Wed, 21 Mar 2007 15:25:57 -0500
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Date: 2007-03-21T15:25:57-05:00
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<adaworks@sbcglobal.net> wrote in message
news:4eeMh.16400$bb1.2557@newssvr17.news.prodigy.net...
...
>Units
> in Ada, including declare blocks (which ought to be used minimally)
> have the option of being named.

While I generally agree with Richard, I certainly don't agree on the "ought
to be used minimally" here.

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. (Sure, one could argue
that the underlying library should be improved to avoid the need for this,
but that isn't always possible and in any case changes to widely used
specifications shouldn't be made lightly. And this is just one example, any
sort of temporary has these sorts of requirements.)

The advantage is that if in the future you find that you no longer need the
temporary, you can remove it without heavy code analysis: it is used only in
the one place and there is no worries that it might be reused, or have a
side-effect, or the like.

                        Randy.