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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: container cursor type cannot be tagged
Date: Fri, 29 Aug 2014 18:00:56 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2014-08-29T18:00:56-05:00
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"Stephen Leake" <stephen_leake@stephe-leake.org> wrote in message 
news:85d2bjxscf.fsf@stephe-leake.org...
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>> That seems to make more sense, honestly. But how are you dealing with the
>> "can't have two tagged types" problem for the container itself?
>
> I don't see the problem; I declared my container with tagged container
> and cursor, and only had a problem when I tried to instantiate
> Ada.Iterator_Interfaces.

How did you do that? Any operation that takes a container and a cursor is 
illegal if both are tagged. I don't see how you could have a constructor for 
a cursor in that case (it must at least take a container and return a 
cursor), and operations involving container updates could work as 
cursor-only operations but are dangerous (because they would allow writing 
constant containers).

Using Cursor'Class in this circumstance is a lie (there never will be any 
derived types that work) and of course forces checking to runtime (or not at 
all).

                                  Randy.