Hi Nick,
On Fri, Jan 21, 2011 at 12:41 PM, Nick Sutterer <apoton...@gmail.com> wrote:
> According to the docs, class_attribute does implement inheritance for
> class instance variables. However, it doesn't work as it is intended
> to, at least if you use "mutual structures", like Hash.
>
> Base.foo = {}
> Subclass.foo[:bar] = "bar"
>
> Base.foo # => {:bar => "bar"}
>
> I'm sorry, but this is WRONG and dangerous. The docs tell me to "use
> setters" here - not sure how this is supposed to work.
>
> Another "solution" is to initialize the ivar in the subclass, again,
> as done here: https://github.com/rails/rails/commit/09195f10bd3
>
> SO, if I need to initialize the ivar, I don't need inheritance. Why is
> that called "inheritance" at all?
>
> By accident I solved this with a 10-liner months ago, why not use
> something like that?
> https://github.com/apotonick/hooks/blob/master/lib/hooks/inheritable_attribute.rb
>
> It's simple, clean and does exactly what you expect.
>
>
> I just found out class_attribute nearly broke my code, so all I want
> is prevent people from stepping into that trap, too :-D
>
> Cheers!
# To modify an inherited hash in-place, each subclass needs its own
copy up-front. Use class_inheritable_attribute for this
copy-on-inherit behavior.
class Base
class_inheritable_attribute :options
self.options = {}
end
class Subclass < Base
self.options[:foo] = 'bar'
end
# Use class_attribute for inheritance that behaves just like Ruby
methods. The superclass value is used unless it's overridden by a
subclass' value.
class Base
class_attribute :options
self.options = {}
end
class Subclass < Base
self.options = self.options.merge(:foo => 'bar')
end
# With a declarative API
class Base
class_attribute :options
def self.config(options) self.options = (self.options ||
{}).merge(options) end
end
class Subclass < Base
config :foo => 'bar'
end
Jeremy
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