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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Streams and Concurrency
Date: 1999/01/04
Message-ID: <EACHUS.99Jan4145726@spectre.mitre.org>#1/1
X-Deja-AN: 428735839
References: <76c3tv$acs@bgtnsc02.worldnet.att.net>
 <76cat4$2ldc$1@news.gate.net> <76dn7b$a35@bgtnsc03.worldnet.att.net>
 <76e4rg$bsr$1@nnrp1.dejanews.com>
Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.ada
Date: 1999-01-04T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <76e4rg$bsr$1@nnrp1.dejanews.com> dennison@telepath.com writes:

 > But this solution only works for objects that are part of the same class
 > hiearchy. That's too restrictive. I'd want to be able to use any type. It
 > sounds like Tuck's generic suggestion is the way to go.

   Wonderful opertunity for generic children. ;-)  Create a (generic)
package that encapsulates the stream and the locking mechanism.  This
package would then have a generic child package that you instantiate
once for each type you want to write to the stream.  (And now for the
really tricky part...)

   If you want to be able to read the mixed stream without knowing
what type of value appears next, you have to have a parent type in the
parent generic, or a parent access type, and a read operation declared
there which returns objects of the class rooted at this type.  You can
then use a fairly common Ada idiom (a declare block with a class-wide
object initialized by a function) to make the contents of the stream
available.

   The case where you know the structure of the stream, or as Tucker
suggested, have markers in the stream, is much easier to program.

      
--

					Robert I. Eachus

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