Re: Eiffel and Java + Ada dispatching

[donh@syd.csa.com.au (Don Harrison)]

Robert I. Eachus writes:

:   In Ada you get to choose between THREE places where parameters and
:methods can be fixed:  At the point where generic definition appears,
:at the point where the generic instantiation occurs, and at the point
:of the call.  

That sounds about the same as Eiffel.

:The "tricky bit" is that you can also have overridable
:defaults bound at any of those three locations.  I don't know why you
:would want to provide a RK routine where the default number of steps
:was set during instantiation, but you can do it if you want to.

I'd have to say that I never instantiate anything in Ada without explicitly 
providing actual parameters. I think it makes it easier to see what's going 
on at the instantiation site without having to check the generic declaration 
to see that a default isn't unwittingly being used. So, rather than being 
disappointed that Eiffel doesn't have default actual parameters, I'm glad 
that it doesn't.

:  > If you were writing this now in Ada95, would you be able to reduce
:  > the complexity by using OO stuff?
:
:   No, and no!  First, the complexity is not in the code, it is in the
:understanding of the requirements.  Second, if those are the
:requirements, the same solution is probably the simplest in Ada 83 and
:Ada 95.

I'll take your word for it. 

:   This is a symptom of a general problem for OO programmers learning
:Ada.  In Ada generics are often a much simpler, and hugely more
:maintainable solution to many problems that can only be solved with
:inheritance in other OO languages.  

Yes, generics are useful. I'm glad they are in Eiffel. However, if I had to
choose between generics and inheritance, I would choose inheritance. I recall
Bertrand Meyer saying in OOSC that you can emulate generics using inheritance
but not the reverse.

:  > I'll interpret 'powerful' to mean 'esoteric'. :)
:
:  No, I meant powerful.  Just like working with rocket fuel or
:high-voltage electicity or what have you.  When you are working with
:constructs where the change of one word, say a parameter name, can
:have a global effect on modules which never use that name, you have to
:use design principles and configuration manangement tools very
:different from the run of the mill.

If it's all the same to you, I'll stick to 'the run of the mill'. :)


Don.
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Don Harrison             donh@syd.csa.com.au