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From: Jeff Carter <jrcarter001@my-deja.com>
Subject: Instantiating a generic formal procedure with an access procedure
 value
Date: 1999/12/31
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Date: 1999-12-31T00:00:00+00:00
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Here's something that I haven't been able to figure out from the ARM.
No doubt I haven't looked in the right place yet.

Suppose I have a package that provides an unprotected structure
(normally this would be a generic package, but that's not important for
this example):

package S_U is
   type Handle is limited private;

   procedure Op (Item : in out Handle; Item : in Integer);

   generic -- Iterate
      with procedure Action
         (Element : in out Integer; Continue : out Boolean);
   procedure Iterate (Over : in out Handle);
private -- S_U
   ...
end S_U;

Suppose I now want to use this package to create a protected structure:

with S_U;
package S is
   type Action_Ptr is access procedure
      (Element : in out Integer; Continue : out Boolean);

   protected type Handle is
      procedure Op (Element : in Integer);
      procedure Iterate (Action : in Action_Ptr);
   private -- Handle
      Data : S_U.Handle;
   end Handle;
end S;

package body S is
   protected body Handle is
      procedure Op (Element : in Integer) is
      begin -- Op
         S_U.Op (Item => Data, Element => Element);
      end Op;

      procedure Iterate (Action : in Action_Ptr) is
         procedure Local is new S_U.Iterate (Action => ???);
         -- What do I use here?
      begin -- Iterate
         Local (Over => Data);
      end Iterate;
   end Handle;
end S;

Neither Action nor Action.all will compile here. The only thing I've
found that will compile is

procedure Iterate (...) is
   procedure Dummy (Element : in out Integer; Continue : out Boolean) is
   begin -- Dummy
      Action (Element => Element, Continue => Continue);
   end Dummy;

   procedure Local is new S_U.Iterate (Action => Dummy);
begin -- Iterate
   Local (Over => Data);
end Iterate;

Hopefully there's a way to avoid this extra procedure call.
--
Jeff Carter
"Now go away or I shall taunt you a second time."
-- Monty Python and the Holy Grail


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