Another newbie question

[Mike Meyer]

Steven D'Aprano <steve at REMOVETHIScyber.com.au> writes:
> On Wed, 07 Dec 2005 23:58:02 -0500, Mike Meyer wrote:
>> "solaris_1234" <solaris_1234 at yahoo.com> writes:
>>> 1)  The stmt "board.Blist[10].DrawQueen(board.Blist[10].b1)" seems
>>> awkward. Is there another way (cleaner, more intuitive) to get the
>>> same thing done?
>> Yes. Reaching through objects to do things is usually a bad idea. 
> I don't necessarily disagree, but I don't understand why you say this. Why
> it is bad?

Such behavior couples you to the objects you use very tightly. This
makes it harder to adapt those objects to changing needs. One popular
rule of thumb is the "Law of Demeter". Googling for that will turn up
lots of information.

My standard object interface is modeled after Meyer's presentation in
OOSC: an objects state is manipulated with methods and examined with
attributes; manipulating attributes doesn't change the internal state
of the object. This makes it possible to change the internal
representation of a class without having to change all the clients of
the class to match.

>> Some languages don't allow you to do that at all; 
> Fortunately we aren't using "some languages", we're using Python, and so
> we aren't forced to fill our classes with helper functions when we can
> simply call the object methods directly.

Yup. I'm not pushing for a change in Python to suit my design
goals. If I feel the need for languages that enforce my design
decisions, I know where to find them.

      <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.