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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Simpler question, create instance of unknown tag
Date: 1996/03/15
Message-ID: <dewar.826948716@schonberg>#1/1
X-Deja-AN: 143316988
references: <DoBw6H.Lyv@plato.ds.boeing.com>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-03-15T00:00:00+00:00
List-Id: <comp.lang.ada>

Scott asked:

"  Can one use an Ada.Tags.Tag  value (call it a meta-type)
  and dynamically use it to create a concrete object
   where the new object'Tag = this_tag_value

The compilers definitely can do this (for the Input implementation)
but can us mortals do it?"

No, there is no way to do it, and I have found several times that this
is a minor irritation. For the most part, GNAT translates the stream
attributes into legitimate lower level Ada, but it can't do that for
Input (see GNAT sources for details on the very interesting "kludge"
needed to implement this feature).

It's hard to think of a nice syntax for adding this to the language?