Re: Redefined "=" = generic disaster?

[Vincent Marciante <marciant@li.net>]

Jeff Carter wrote:
> 
> Vincent Marciante wrote:
> > Ugh!  So _are_ you saying that the Ada 83 code was defective wrt. Ada
> > 83?
> 
> In Ada 83, you could not redefine "=" for any type that could be used to
> instantiate the generic, so if you wrote "=" in the generic, it meant
> you wanted the predefined "=" for the type.

My point is that in Ada 83, if predefined "=" of a type did not agree
with the concept of equality that a designer intended for the type then
that designer should have eliminated it by declaring the type as
limitted private thereby not allowing it to be used to instantiate a
generic designed by someone else that imported a simple private type (I
say safely assuming that if the predefined "=" is available then it is a
semanticly correct eqality.)

(the first way that I tried to clarify my point follows - I'm still not
sure if either is clear enough, that why I didn't delete it.)

I understand this.  My point is that in Ada 83, if some one wanted to
create one ADT whose semantics required changing the condition for
equality then because it _had_ to be made limited private, the creater
of _some_another_ ADT could depend on the fact that even though a formal
equality operation was _not_ expliciely specified in _his_ ADT, using
the "=" associated with any formal private type was safe!  Or stated the
other way around, if the first guy's ADT's semantics were such that the
value returned by the predefined "=" for his type did not agree with the
semantics of the ADT that he was trying to design, then allowing "=" to
continue to exist (by not having used a limitted private type) would be
considered a defect in _his_ ADT - not a defect in an Ada 83 generic
unit that imported a mear private type (and implicitely assumably
semanticly correct equality operation of the type used to instantiate
his generic unit.) 

Do you see that I think that I am seeing a subtle issue about what could
be assumed in Ada 83 verse Ada 95.  


> This is still the case in
> Ada if you do not explicitly import "=". If, in Ada 83, you wanted some
> other behavior than the predefined "=", you still had to import it:
> 
> with function Equal (Left : T; Right : T) return Boolean;
> 
> The only real change in Ada is that now you can use the infix "=" to
> represent user-defined equality, while in Ada 83 you had to use
> something less intuitive. In either language, you get the predefined "="
> if you don't import something else, and have to import something else if
> you don't want the predefined behavior.
> 
> --
> Jeff Carter
> "I waggle my private parts at your aunties."
> Monty Python & the Holy Grail