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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Perhaps we keep lists elements private and adjust the elements to
 fit?
Date: 23 Jul 2002 15:23:04 -0400
Organization: NASA Goddard Space Flight Center (skates.gsfc.nasa.gov)
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"Chad R. Meiners" <crmeiners@hotmail.com> writes:

> "Stephen Leake" <stephen.a.leake.1@gsfc.nasa.gov> wrote in message
> news:uheirlk4z.fsf@gsfc.nasa.gov...
> > My own opinion is that supporting limited types is a requirement for
> > any general-purpose container.
> 
> Perhaps what we need to do is write the container libraries to accept
> private types and provide a generic package that converts limited privates
> to private types.  Let's assume that we have a limited type as follows

> <snip interesting proposal for wrapper package>

"Promoting" a limited type to a private type by adding a generic
"copy" operation is certainly one way to go. 

In SAL, I allowed for "true" limited types, where copy makes no sense
in any situation. The container packages require a "Copy" operation,
but for "true" limited types, the user simply provide a "copy" that
raises an exception.

Also in SAL, I have helper packages that define the obvious "copy"
operation for a non-limited type.

I guess we could have a couple versions of the generic "promote"
package; one that does a simple copy, one that raises an exception.
Users could write others that do deep copy, etc. That might be better
than what I have in SAL now.

-- 
-- Stephe