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

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

(A bit of explanation on my last post). I wrote:

:I think the choice in Eiffel of making specialisations functionally equivalent
:to their generalisations is the right one in terms of modelling integrity.

By 'functionally equivalent to', I mean 'polymorphic wrt'. 

The issue of modelling integrity implies a pragmatic consideration as well.
If specialisations reflect greater modelling integrity, you would also expect
that specialised operations are what you would want to *use* (call) most of the 
time rather than general ones. It makes sense, then (to maximise the power of
dynamic binding), for them to be polymorphic wrt the parent class. I don't
have any data to back this up but it seems logical. (if someone can confirm
this, please share it with us).

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.


I should also clarify the following.

: ... So, Eiffel 
: dispatches to a more specific operation by default rather than to a more general 
: one.

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. 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. 

and

: So, Ada dispatches to a more general operation by default rather than to a 
: more specific one. ... 

should read

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


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