Class variables in RubyEdit

Differences between class variables and instance variables:

• @@foo: shared by a class and all its subclasses
• @foo:
  • on an instance method, becomes an instance variable
  • on a class method (or an instance method of a metaclass), becomes a class variable visible only to the class (ie. not shared with subclasses)

Example:

class Parent
  @@foo = 1

  class << self
    def bar
      @bar ||= 10
    end
  end
end

class Child < Parent
  def foo
    @@foo # returns 1, the value of @@foo from the superclass
  end

  def self.bar
    @bar ||= 20 # not shared with superclass
  end
end

Parent.bar # => 10
Child.bar  # => 20