Re: OO should break when broken

[Colin Putney <address@hidden>]

I've snipped large parts of Vesa's post, mostly because he objects to 
the simplifications I made in order to keep my argument short, but does 
not explicitly disagree with my conclusion. Again, I think shapes are 
not a good example to use in discussions of object modeling, because 
the mathematical classification of shapes that everyone is familiar 
with does not map to a class hierarchy that models those shapes well.

Vesa, do you disagree with this conclusion, or just my argument in 
support of it?

On Monday, September 1, 2003, at 04:01  PM, vkarvone@mappi.helsinki.fi 
wrote:

> Stated in another way, the essense of a subclass is to constrain the 
> set
> of states of the superclass.

Interesting. Would you care to give an example, or explain why you 
believe this?

> 2. One just can not generally ignore behaviour (= functions and 
> procedures)
> when dealing with software. Representational (data) hierarchies are 
> useless
> unless they satisfy useful invariants that can be exploited by 
> behavioral
> entities (= functions and procedures).

Sure. But it's not terribly useful to talk about behaviour unless you 
have an idea of the function the software is to perform. So basically, 
the whole discussion boils down to "it depends on your application." 
For sake of argument, assume that all the shape classes have to 
implement a simple interface: #width, #height and #draw.

Colin