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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Fri, 5 Apr 2013 20:45:40 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:14885
Date: 2013-04-05T20:45:40-05:00
List-Id: <comp.lang.ada>

<Stefan.Lucks@uni-weimar.de> wrote in message 
news:alpine.DEB.2.02.1304052103590.31746@debian...
...
>OK, here we agree. Whatever the "new" strings are, the ability to define
>incompatible types with the same representation, that you cannot mix
>(without explicit conversion) is important for a language supporting
>safety-critical stuff! I sometimes have types Tainted_String and
>Save_String, being both derived from [Wide_[Wide_]]String, and I am happy
>when the compiler stops me from messing up between variables of this type.
>Does Randy's proposal really not allow that?

Of course they're different types. They wouldn't be mixable amongst 
themselves (Dmitry's obcession with multi-methods would of course erode any 
such protections).

They both would implicitly convert to Root_String'Class, of course, and 
there wouldn't be any way to prevent that. But I can't see any particular 
new problem with this, you have the same effect for any Ada tagged type and 
associated class-wide type.

I know Dmitry would like to have some sort of way to split off clones of 
types that are completely incompatible, but that would have severe 
consequences with the other uses for type hierarchies (conversions and 
formal types), as those could not be allowed either.

                                                  Randy.