Copy constructors

[Alex Martelli]

"Glyph Lefkowitz" <glyph at twistedmatrix.com> wrote in message
news:mailman.997561650.27157.python-list at python.org...
    ...
> Am I correct in understanding from this thread that there is an intent to
> remove the ability to assign an instance's __class__ attribute?

That's how I'm reading Guido's messages in this thread, too.


> > Let's just say that use of this feature is at your own risk.  It was
> > an experiment.  I *could* restore it partially (see below) but I'd
> > rather not, given that better alternatives are available.
    ...
> Also, as far as I know, better alternatives do not exist; for example,
> "promise" objects from a database which are latently initialized when they
> are accessed.  One module that I use *all the time*;

I don't know of any better way to handle the Promise design pattern,
either.  In C++, I'm having to kludge around it all the time via
letter/envelope idioms -- the possibility of changing classes on
the fly makes it much simpler and more direct.  Hadn't thought
of that earlier...

> twisted.python.rebuild.rebuild, is based entirely upon this "trick".  One
> of the eye-popping cool features of Python is the ability to change code
> and have existing instances update to use the new methods automatically.

That one seems to be related to _another_ capability (of which I've
seen no indication that it's also going away) -- keeping the same
class object. but changing that object (rebinding method attributes
thereof).  Or maybe I don't understand exactly what you mean?


> Smalltalk's Object>>become: is highly useful for similiar reasons; is
> there a new way to emulate this without __class__ assignment?

It seems to me the functionality of become is homomorphic to that
of class-assignment, unless I'm truly missing something major.


Alex