Re: Your wish list for Ada 202X

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1wchtiw4r35px.1pwedxqesqlr4.dlg@40tude.net...
...
>> (A) we're specifically talking about a single addition or deletion, *not* 
>> a
>> general "change".
>
> And how is it different from single dispatch? Let you override f in S. 
> Then
> f(X), given X is of S, will call to the new body.

"overriding" is a change of an existing operation, not what I'm talking 
about here.

>> (B) Of course we're changing the specification and recompiling. But we 
>> don't
>> want the same client code to mean something different after that
>> recompilation without detection -- in the case of a single addition or
>> deletion (again, *not* a change).
>
> It must mean something different. That was the *purpose* of the change to
> make the client code mean it different *when* the clients use the types 
> and
> operations for which the change was made.
>
>> The reason here is that maintainers need to be free to ADD new
>> operations/entities without changing the behavior of any pre-existing 
>> client
>> (which necessarily does not use those new operations/entities).
>
> Again, no difference between SD and MD. If you add a new primitive
> operation (not override an existing one), there cannot be any effect on 
> the
> clients because they did not use the operation.

But that's not now and never has been true. Why? Because the new operation 
can have the same name as some existing operation, and the entire point of 
this discussion is that preference rules in overloading resolution have 
potentially bad effects in such cases.

Anyway, what I get from your responses is that you don't think that there is 
any real issue with maintenance (in that you think a change is a change is a 
change, and if there is a change, then behavior might change). Perhaps you 
are right, but that's been one of the cornerstones of the Ada design since 
the beginning, and abandoning it for convinience would be essentally the 
same as abandoning the "maintainability" goals of Ada.

                                           Randy.