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From: Evans@TL-20B.ARPA ("Art Evans")
Newsgroups: comp.lang.ada
Subject: renaming types
Message-ID: <8706270326.AA26169@ucbvax.Berkeley.EDU>
Date: Fri, 26-Jun-87 13:28:28 EDT
Article-I.D.: ucbvax.8706270326.AA26169
Posted: Fri Jun 26 13:28:28 1987
Date-Received: Sat, 27-Jun-87 14:03:33 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
List-Id: <comp.lang.ada>

Ada does not permit renaming types, the syntax in ARM 8.5 not including
any way to do so.  In general, the rationale for this lack is that a
subtype declaration can be used instead.  However, using a subtype does
not work in all cases.

What I want is something like this:
	with B;				-- Package exporting a type.
	package A is
	   type T is private;		-- A private type.
	   ...
	private
	   type T renames B.BT;		-- Illegal!
	end A;
The renaming declaration is of course illegal.  Moreover, the subtype
mechanism doesn't help, since there's no such thing as a 'private
subtype' declaration and a private type may not be completed with a
subtype.

I see no clean way out of this problem.  The problem can be solved (sort
of) by completing the private type declaration with either of 
	   type T is record
	      F: B.BT;
	   end record;
or
	   type T is access B.BT;
I find both of these to be pretty ugly.  Either affects all code that
uses objects of the type.

Has anyone a better solution?  This matter looks like a candidate for
consideration when Ada is next revised.

Art Evans
Tartan Labs
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