At 6:53 PM +0100 4/8/04, Mark Sparshatt wrote:The problem, as far as Ruby is concerned, is that it has two subtly different types of class variable.
It seems that for Ruby instance variables can be modelled using attributes, but I couldn't see any way of handling class variables. So, what is the recommended way of handling them?
First, one takes the bat labeled "Metaclasses" and smacks the designer in the head with it. Then, once enlightenment has hit, we implement metaclasses and you add class variables as new attributes on a class' metaclass. I think.
there are metaclass instance variables, which would be created using this piece of evil looking code
class Example
class << self
attr_accessor :x
end
endthe class << self part accesses the metaclass Example' and then adds accessor methods to access it's instance variable x.
However when talking about class variables in Ruby you usually mean variables that are accessed using the notation @@x
The difference between these two methods is that if created a sub class SubExample, using the metaclass instance variable method changing SubExamples value of x wouldn't affect Example's copy. Whereas if you used the class variable method, then changing @@x in SubExample does affect the value of @@x within Example.
This is starting to sound like one of the less pleasant parts of Ruby :P.
Alternately you can stick 'em in as plain variables in the class namespace, which is probably the right answer for the moment, though not for the long run.
Thanks, that does seem to be the best way to deal with the @@variables.
-- Mark Sparshatt
