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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: List container strawman 1.2
Date: 13 Nov 2001 14:10:31 -0500
Organization: NASA Goddard Space Flight Center
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Date: 2001-11-13T19:13:09+00:00
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"Martin Dowie" <martin.dowie@nospam.baesystems.com> writes:

> "Ted Dennison" <dennison@telepath.com> wrote in message
> news:3BECA3B7.5020702@telepath.com...
> [snip]
> > --------------------------------------------------------------------------
> -----
> > -- This file contains a proposal for a standard Ada list package.
> > --
> > -- version - Strawman 1.2
> > --------------------------------------------------------------------------
> -----
> > generic
> >     type Element is private;
> > package Containers.Lists.Unbounded is
> 
> Hmm, how about adding two lines to this to allow a list to be specified
> as having 'unique' items or not? e.g.
> 
> generic
>     type Element is private;
>     Elements_Must_Be_Unique : Boolean;
>     function "=" (L, R : Element) return Boolean;
> package Containers.Lists.Unbounded is
> 
> I have found this to be very useful in the past - but this may
> have just been the specifics of the problem domain I was working
> in.

Actually, I prefer three choices for "duplicates"; ignore, error, and
allow.

I use "ignore" when I'm accumulating lists of Ada packages to "with"
(in an ASIS application); each package is on the list only once.

I use "error" when the program logic forbids duplicates; lists of
people, for example.

I use "allow" in other situations, usually when "compare" actually
makes no sense (a list of GUI controls).

This feature is not yet in my on-line version of SAL; I have not been
keeping it up to date.

-- 
-- Stephe