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From: mheaney@on2.com (Matthew Heaney)
Newsgroups: comp.lang.ada
Subject: Re: Charles: Generic_Find
Date: 13 Nov 2002 11:18:38 -0800
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porton@ex-code.com (Victor Porton) wrote in message news:<3dd082fe$0$307$bed64819@news.gradwell.net>...
> Why Generic_Find is generic? Why not just pass the predicate
> as a function access? Doing so would avoid the need of
> generic instantiation. I suggest to change this.

The generic version of find is generic because Ada doesn't have
downward closures.  You have to be able to do something like this:

type Employee_Type is
   record
      SSN : SSN_Type;
      ...
   end record;

Employees : Container_Subtype;

function Find (SSN : SSN_Type) return Iterator_Type is
 
   function Predicate (E : Employee_Type) return Boolean is
   begin
      return E.SSN = SSN;
   end;

   function Find is 
     new Generic_Find (Predicate);
begin
   return Find (First (Employees), Back (Employees));
end;

Function pointers exist in Ada to implement callbacks, from say, a
GUI.  Unless you need a callback, you should be passing subprograms as
generic formal subprogram parameters.

Your suggestion is noted, and rejected.

Matt