Re: Eiffel and Java

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

Matthew Heaney writes:

:Ada's type mechanism accomplishes the equivalent of pre- and
:post-conditions, and you don't seem to mind their inclusion in Eiffel, so
:that can't be it.

It's true that Ada's typing does accomplish some of what assertions offer 
but assertions are more general (and useful) than that. For example, it is
possible to specify that *any* boolean condition on a parameter must hold - 
not just that it belongs to a particular family of types or that it's value 
satisfies a range constraint.

Any of a number of Eiffel books provide more info.

:About subprogram calls.  C++ or Eiffel programmers call objects this way:
:
:   theStack.push (5);
:
:and Ada programmers do this
:
:   Push (5, On => The_Stack);
:
:It's not a moral issue which way is better, just a difference in syntax. 
:They both do the same thing.

Yes - not something to lose sleep over. The Ada syntax can be justified
because it is a hybrid language. IMO, the dot notation is preferable for
Eiffel because it is a pure, single-dispatched language. For such
languages, it makes sense to isolate the dispatching parameter to show that
it is special. The downside is that symmetric operations do not appear as
such. Well, not really, because you can always regain it by inventing another 
class for performing symmetric operations:

eg. class SET_OPS
      ...
      union (a, b: SET): SET is ...
      intersection (a, b: SET): SET is ...
      ...
    end

In any case, truly symmetric operations are relatively few, IMO.


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