[Zope3-dev] Notations for paths

[Phillip J. Eby]

At 05:12 PM 12/19/02 -0500, Guido van Rossum wrote:
> > > 1) shuffle around tuples for something that *isn't* a tuple
> >
> > But it is! It's a sequence of steps for traversal.
>
>Then it should be a list.  Tuples should be used for fixed-length
>heterogeneous sequences.  Lists for variable-length homogeneous
>sequences.

Great!  Now in addition to parsing errors, we can have errors caused by 
accidentally modifying shared mutable objects.  Zope 3 applications will 
then be even *more* fun to debug than Zope 2 applications...  if you're a 
masochist, anyway.  ;)

IMO, immutability is an application framework's first line of defense 
against "how the heck is *that* happening?" errors by the framework's 
users.  Raising errors early (as would happen when an API tries to coerce 
an invalid location object) is the second.

I'd say I don't really care about this because I'm not the one who'll have 
to support Zope 3, but that's not really the case.  I *will* be the person 
supporting Zope 3 for my development staff, and occasionally people in 
other parts of the company I work for as well.  That's why I'm -0 on using 
simple types where a framework-specific interface is desirable, and -1 or 
more on using mutable types anywhere that "value" semantics are 
desired.  These are both near the top of my hypothetical list of the "top 
10 ways to mess up users of a framework and make their programs hard to debug".