Re: Assignment of limited private types...

[hbaker@netcom.com (Henry Baker)]

In article <3gjce1$1he@theopolis.orl.mmc.com>, "Theodore E. Dennison"
<dennison@escmail.mmc.orl.com> wrote:

> stevem@dcs.gla.ac.uk (Steve McGowan) wrote:
> >
> > I'd like to pass in a 'file_type' identifier into a task, make a local
> > copy of this identifier within the task, and then write text to this
> > file stream inside the task.
> > But I cannot do this since 'file_type' is limited private.
> > Any ideas how I can pass in this identifier, and to write to it
> > locally?
> 
> The reason people make types "limited private" is so users CAN'T 
> make local copies of the objects. If the designer wanted you to
> be able to make copies of file_type objects, she would have made
> the type "private".

That may have been the original intent, but that isn't what Ada ended
up with.  What you describe requires a _read_ barrier, but Ada only
gives you a _write_ barrier.  Limited private types can't be assigned
to, but can easily be read from, and 'copies' made.

Put your WWW browser onto the following URL's for more background on limited
private types:

ftp://ftp.netcom.com/pub/hb/hbaker/LimitedRoots.html (or .ps.Z)
ftp://ftp.netcom.com/pub/hb/hbaker/LimitedRobbery.html (or .ps.Z)
ftp://ftp.netcom.com/pub/hb/hbaker/LPprogram.html (or .ps.Z)