Re: Reemergence of predefined equality operator...

[Vincent Marciante <marciant_remove@earthlink.net>]

Robert A Duff wrote:

<snip> 
 
> If you wanted to drive a stake through the heart of the predefined "="
> by declaring a user-defined "=", so that every time objects of type T
> are compared for equality it will call the user-defined "=", then you
> lose -- if you pass T to a generic or wrap T in a record, the predefined
> "=" reemerges (rises from the dead).
> 
> For "=", this seems "obviously" wrong.  But as I pointed out elsewhere,
> the situation for other operators (eg, "mod"), is not so obvious.
> Even if the language were changed, or even if Text_IO.Integer_IO took
> "mod" as an "is <>" parameter as above, it's not clear (to me) what the
> right answer is.

The crux of the problem in this specific case (generic private types) 
seems to me to be _not_ reemergence but actually the new (Ada 95)
permission
to override predefied "=".  (Allowing the definition of "=" with a 
non-boolean result does not seem to be a problem.)

If overriding of predefined "=" was disallowed in the future (not
practical?) wouldn't that solve the problem well?   Is that really
really not practical?

Vincent Marciante