Copy constructors

[Glyph Lefkowitz]

On Sat, 11 Aug 2001, Guido van Rossum wrote:

> "Alex Martelli" <aleaxit at yahoo.com> writes:
> 
> > I call the feature 'rarely used', but others may use it less
> > rarely.

For example, me.

Am I correct in understanding from this thread that there is an intent to
remove the ability to assign an instance's __class__ attribute?

> 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.

Are there any features that we can use any longer that are not 'at our own
risk'?  Division will be changed, __class__ assignment is going away,
type() means something different, even the rules of scope...

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*;
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.

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

> I'm sure I'd be able to come up with some kind of check that works. It
> would probably be very similar to the check I already use to determine
> whether two base classes are compatible -- the check that stops you
> from doing "class C(list, dictionary)".  But I repeat: I'd rather not.

Is there a discussion somewhere of why you'd rather not?  This is
*essential* functionality for me, especially since it sounds like it won't
be able to be completely replicated through some other mechanism.  (If you
implement "reference.become(other)", for example, I won't mind nearly so
much <0.5 wink>)

> That depends on how much of a slowdown it is. :)

I don't know about others who use this feature, but the way I use it I
could afford to wait 0.5 seconds for each __class__ assignment and not be
too upset about it.  Losing this ability entirely, however, would remove a
significant feature from Twisted when used with a later python version.  
I implore you not to remove it.

maybe-we-ought-to-stop-pretending-that-this-new-language-with-
	different-syntax,-idioms,-and-semantics-for-everything-
	is-really-still-python-ly-y'rs,

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