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- Subject: Re: Re: Still cryptic OOP syntax
- From: David Olofson <david@...>
- Date: Mon, 31 Jan 2005 03:47:51 +0100
On Monday 31 January 2005 02.21, Jamie Webb wrote:
> On Mon, Jan 31, 2005 at 11:42:58AM +1100, skaller wrote:
> > > I did
> > > something similar for the simple types (integer, reals,
> > > anything that doesn't carry an object reference) in the form of
> > > large single level switch that decodes values combined from the
> > > operator and the operand types. Fast and simple, and yet makes
> > > trivial to implement things like "Pascal style
divison" (integer /
> > > integer ==> real, rather than integer).
> > >
> > > The problems gather when you get to operations on objects...
> > Of course. It's impossible. This is the covariance
> > problem I referred to in another post.
> > YOu need n^2 routines for n types, which doesn't fit
> > into the n methods OO allows... this kills OO as a
> > programming methodology with a one line argument.
> It's certainly one of the numerous flaws in Java, but I don't think
> you can dismiss OO in general so easily. Surely in a dynamically
> typed language nothing more than multiple dispatch is required?
Yeah... One that covers all potentially relevant types, and one of
those for each operator.
And if you want both 'this * x' and 'x * this' between objects that
don't have a two-way relation (ie when you add user types that want
to interoperate with core types or types from other extensions),
you'll need reverse operators as well - and obviously, VM support for
The ugly thing about that is that the VM is forced to decide whether
to use a forward or reverse method, based on whether or not the left
hand object has a suitable method. That's at least one extra
conditional in the main path, and some more when that one catches a
What if both operands have methods that would fit...? (Which is the
case when you operate on two objects of the same type; if that method
is implemented, both operands will be equally capable of performing
So, doing this in a "proper" OO way looks more and more like some
//David Olofson - Programmer, Composer, Open Source Advocate
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