Addressing the last element of a list

[Mike Meyer]

Antoon Pardon <apardon at forel.vub.ac.be> writes:
> Op 2005-11-10, Mike Meyer schreef <mwm at mired.org>:
>> [Context recovered from top posting.]
>> "bonono at gmail.com" <bonono at gmail.com> writes:
>>> Daniel Crespo wrote:
>>>> Well, I hope that newcomers to Python don't confuse himselves :)
>>> This mutable/immutable object and name/variable is confusing.
>> Only if you have to overcome a conviction that variables behave in a
>> different way. If you've never seen them behave another way, or have
>> already gotten used to this model from another language (it dates back
>> to the 60s, if not the late 50s), then it's no problem. I'm sure the
>> problem exists in the opposite direction, except that few people
>> travel that route.
>> Most OO languages do the name/variable thing, but some of the popular
>> ones aren't consistent about it, giving some types "special" status,
>> so that sometimes "a = b" causes b to be copied onto a, and sometimes
>> it causes a to become a pointer to b. I find a consistent approach is
>> preferable.
> But what about a consistent approach, that allows choice.

It's been done in other languages. But it requires more care than one
would think.

> Like having an assignment operator (let use @= for it) next to a
> (re)bind operator.
>
> We could then have something like the following.
>
> a = 5
> b = a
> a @= 7
> b ==> would result in 7.

You've just overwritten the object referred to by the token "5" in the
source code with the value 7, so you get:

print 5
7

Not exactly a desirable outcome, but some language implementations
have allowed this kind of thing in the past. You either have to make
all objects mutable, or disallow assignment to immutable objects,
which sort of defeats the purpose.

Another approach is to have a special object type if you want to allow
assignment to the object it refers to. That's what Python does now, it
just doesn't have a syntax just to support that. If it did, your
example might look like:

a := 5
b = @a
a := 7
@b ==> would result in 7

   <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.