[Edu-sig] Design Patterns

[Arthur]

>In my MVC example, the Viewer expected a 'shape' object to support a
>specific API:  verts and edges needed to be available as attributes.  

Let me try to practice better what I think I am preaching and follow your
lead in making the discussion more concrete and less theoretical.

I have a line segment - defined as the segment connecting 2 points.  The
interface allows the points to be picked and moved.

The line segment has a length.  I choose line.getLength() as my API which I
feel idiomatically expresses in Python that we are calculating the length as
it happens to be when the call is made.  I could quite easily wrap it in a
property function and have a line.length attribute - but find it less
expressive. 

Am I - in fact - violating the Uniform Access Principal. 

If I am, am I violating good programming practice?

If I am in violation of the UAP principal, but not in violation of good
programming practice - what are the bounds of the UAP principal.  And how do
we teach that?

If I am not violating the Uniform Access Principal how do we express on what
basis I am not?

Art