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From: Anton Gibbs <agibbs@dera.gov.uk>
Subject: Subverting 'Access for Sub-programs
Date: 1999/08/03
Message-ID: <37A71EF1.2201@dera.gov.uk>#1/1
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Newsgroups: comp.lang.ada
Date: 1999-08-03T00:00:00+00:00
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Dear Ada Community,

Can someone please advise me on the best way to subvert the language
rules that prevent the use of 'Access on a locally declared procedure ?

For normal objects it is possible to use 'Unchecked_Access but for
sub-programs this is not allowed.

"Why does this idiot want to do this ?" I hear you ask.

Well it seemed reasonable enough to me within a wider application, the
essence of which I have distilled into a few lines below.

package Database is
   type Action_Type is access procedure( I : in Integer );
   -- Perform calls Action for every entry in the database
   procedure Perform( Action : in Action_Type );
end Database;

with Database;
with Text_IO;
procedure Main is
   procedure Print_If_Even( I : in Integer ) is
   begin
      if I rem 2 = 0 then
         Text_IO.Put_Line( Integer'Image( I ) );
      end if;
   end Print_If_Even;
begin
   Database.Perform( Action => Print_If_Even'Access );
end Main;

The offending statement is the one containing the 'Access because
Print_If_Even is declared at deeper level than it.

So how can I achieve what I need here (ie. visibility of parameter I)
without either: a) using global data and making the whole thing
unnecessarily non-reentrant; or b) recourse to the usual generic
contortions which I thought Ada95's procedure access types had allowed
us to escape from ? I am sure someone else must have run into this
problem before and that there is an accepted way of tackling it.

Thanks for any help you can offer.

Best regards

Anton Gibbs.
Software Engineer

-- 
Civil Air Traffic Management Group
Defence Evaluation and Research Agency
Bedford, UK

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