Another newbie question

[Alex Martelli]

Mike Meyer <mwm at mired.org> wrote:

> > "In addition to the full set of methods which operate on the coordinate as
> > a whole, you can operate on the individual ordinates via instance.x and
> > instance.y which are floats."
> 
> That's an API which makes changing the object more difficult. It may
> be the best API for the case at hand, but you should be aware of the
> downsides.

Since x and y are important abstractions of a "2-D coordinate", I
disagree that exposing them makes changing the object more difficult, as
long of course as I can, if and when needed, change them into properties
(or otherwise obtain similar effects -- before we had properties in
Python, __setattr__ was still quite usable in such cases, for example,
although properties are clearly simpler and more direct).

You could make a case for a "2D coordinate" class being "sufficiently
primitive" to have immutable instances, of course (by analogy with
numbers and strings) -- in that design, you would provide no mutators,
and therefore neither would you provide setters (with any syntax) for x
and y, obviously.  However, a framework for 2D geometry entirely based
on immutable-instance classes would probably be unwieldy (except in a
fully functional language); as long as we have a language whose normal
style allows data mutation, we'll probably fit better into it by
allowing mutable geometrical primitives at some level -- and as soon as
the mutable primitives are reached, "settable attributes" and their
syntax and semantics come to the fore again...


Alex