Re: To overload or not to overload (was Eiffel and Java + Ada dispatching)

[jsa@alexandria (Jon S Anthony)]

In article <E0J76n.Evn@syd.csa.com.au> donh@syd.csa.com.au (Don Harrison) writes:

> If it's true that specialisations *are* the operations you want most
> often, then making the general (inherited) operations polymorphic
> means that dynamic binding is wasted on a minority of calls.

First, there is no evidence for this.  Second, the conclusion you draw
doesn't follow anyway.


> should read
> 
> ... So, Eiffel 
> dispatches to a more specific operation by default and does not
> inherit the more general parent operation. However, if you *do* want
> the parent operation as well, then you can repeatedly inherit it and
> leave one the same and specialise the other.

Yes, but that doesn't eliminate the type safety issues.


> This is where Eiffel is very flexible compared with Ada because you
> can nominate *either* the inherited (parent) operation *or* the
> specialised one to be polymorphic wrt the parent.

I don't know why you keep saying this sort of stuff.  You can do this
in Ada as well if that is what you _really_ want.  Just use a class
wide parameter for the non-controlling parameter.  Really, I don't see
the big deal here at all.

    ... Op ( x : P;  y : A'Class )...
...
    ... Op ( x : C;  y : B'Class )...
...
    i : P'Class := ... Something in P's type tree
    j : A'Class := ... Something in A's type tree

    ... Op(i, j) ... dispatch to either P's Op or C's op depending on
                     what sort of thing is in i.  Further, if j is NOT
                     a B thing, then raise constraint error


> should read
> 
> So, Ada dispatches to the general (inherited) operation by default
> rather than to a more specific new one. ...

Well, that's still wrong.  This "default" stuff is completely
irrelevant and has nothing to do with anything in the Ada context.


/Jon
-- 
Jon Anthony
Organon Motives, Inc.
Belmont, MA 02178
617.484.3383
jsa@organon.com