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From: "Ben Brosgol" <brosgol@world.std.com>
Subject: Re: Dispatching and generics - language lawyer question
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Date: 2002-07-25T15:46:45+00:00
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> > For untagged types, _redefined_ equality does not correctly compose and
> > _predefined_ equality reemerges in generics if not properly transferred
by a
> > formal parameter:
>
> But what about "+" and "mod" and so forth?  Package Text_IO.Integer_IO
> probably uses the predefined "mod" to format the number as a string.
> But the *spec* of that package doesn't say that -- it just says the
> string is formatted according to some rules.  If the predefined "mod"
> did *not* reemerge, then a user-defined "mod" operator would break
> Text_IO.Integer_IO.  You may say, "tough luck; that's the programmer's
> fault".  But how should the semantics of Integer_IO be defined in the
> RM?  Surely the use of "mod" there is an implementation detail.

As another interesting case, suppose that you declare an integer type T with
"mod" specified as abstract.  If "mod" on the formal type is invoked from
the generic body, then either the instantiation Ada.Text_IO.Integer_IO(T)
would need to be rejected (a rather flagrant violation of the "contract
model") or else the predefined "mod" would need to reemerge.