Re: Bus error

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> You missed the point. The renaming in my example shall *not* raise
> Constraint_Error. It is a clear language design fault.

Right -- the fact that "X: T renames ..." completely ignores the
constraints on T is a flaw.  There are language-lawyerly reasons for
it...

> Renaming is completely broken in Ada.

A little bit broken.

>...It creates new objects,

Heh?  Renaming does not create new objects.

A function call creates a new object, but that's a
different story.  And it's a good thing -- that function-result
object might need to be finalized, which means it has to be
an object (not just a value).

If I ran the circus, literals would "return" objects, too.
And there would be no syntactic distinction betweem "name"
and "expression".

>... it violates
> contracts,

Not sure what you mean there.  I guess the fact that constraints on T
are ignored, above.  If so, it doesn't violate any contract, so long as
you understand that "X: Positive renames..." is not a contract requiring
positive numbers.  ;-)

>...it introduces names conflicts.

Yes.  We considered fixing that during Ada 9X.

Here's another small complaint about renaming: It's often used as an
"import", as in:

    function Blah (...) return ... renames Some.Library.Package.Blah;

We do not wish to change the name of Blah, just to import it into
another scope.  But mentioning Blah twice is error-prone in that
context.  The programmer really wants to say something like
"import Blah from Some.Library.Package".  Consider:

    function "+"(...) return ... renames Some_Package."+";
    function "-"(...) return ... renames Some_Package."+";

Note cut&paste error on second line.

- Bob