From: Kent Dahl <kentda@...>
Date: 2002-06-26T21:13:58+09:00
Subject: Re: []<<

Tom Sawyer wrote:
> tt['test'] << '..2'         # how come you can do me?

Keep in mind that the first part just returns an object. Once you have a
reference to an object, you can call any method you like on it, that
isn't private or protected. This includes <<.
 
> it seems to me that the main point of accessors and the []= method is to
> control accessiblity to a class' instance variables. right? but as this
> example shows, there are ways in which "back-doors" exist.

If you let your objects out to the surrounding world unprotected (or
unfrozen) these things will happen. Take a look at the dup suggestion
from Jim, or consider freezing your objects before returning them. (This
will mean that you have to create a new object if you want to change it
on the inside, and deny any access on the outside. Sounds like a matter
of preference and optimization consideration.)

Or you could be nasty and do like this before you return:
$ irb
irb(main):001:0> a = [1,2,3]
[1, 2, 3]
irb(main):002:0> class <<a; private :<<; end
Array
irb(main):003:0> a << 5
NameError: private method `<<' called for [1, 2, 3]:Array
        from (irb):3


> shouldn't there be better control of such thing? i came across this when
> i was actually trying to create a []<< method, and realized that i have
> never seen such a beast before! shouldn't such a thing exist?

No. You would then need [](insert any mutator method of the returned
object here) methods, which would drive you bonkers in the end, since
you can't possibly be sure about them all. Freezing or dup-ing sounds
alot more sensible.

-- 
(\[ Kent Dahl ]/)_    _~_    __[ http://www.stud.ntnu.no/~kentda/ ]___/~
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