cattr_accessor in Rails?

It is a rails thing. Basically like the attr_* methods, but for the class level. One thing you wouldn't expect is because it uses a backing @@ variable, the value shared between the class and all instances.

class Foo
  cattr_accessor :bar
end
# => [:bar] 
foo1 = Foo.new
# => #<Foo:0x4874d90> 
foo2 = Foo.new
# => #<Foo:0x4871d48> 
foo1.bar = 'set from instance'
# => "set from instance" 
foo2.bar
# => "set from instance" 
Foo.bar
# => "set from instance" 

For those that stumble across this question too, there is a new way to do this in Rails 3 that works for subclasses:

class_attribute :name

A good blog post on it here.

Defines both class and instance accessors for class attributes

class Person
  cattr_accessor :hair_colors
end

Person.hair_colors = [:brown, :black, :blonde, :red]
Person.hair_colors     # => [:brown, :black, :blonde, :red]
Person.new.hair_colors # => [:brown, :black, :blonde, :red]

If a subclass changes the value then that would also change the value for parent class. Similarly if parent class changes the value then that would change the value of subclasses too.

class Male < Person
end

Male.hair_colors << :blue
Person.hair_colors # => [:brown, :black, :blonde, :red, :blue]

but for Rails 4+ use similar method mattr_accessor, as cattr_accessor is deprecated in rails 4