What does @@ mean in Ruby?

Question

As I'm browsing through a Rails source code, it contains the line:

@@autoloads = {}

What does @@ mean in Ruby?

Answer 1

It means to access a class property (a property namespaced to the class), not an instance one (a property that exists for each instantiated object from that class).

In your example, the @@autoloads will persist for the length of your program.

class TestObj
  @@prop = 0
  def get_prop
      @@prop
  end

  def increment_prop
    @@prop += 1   
  end
end

a = TestObj.new
b = TestObj.new

a.increment_prop 

puts b.get_prop # 1

CodePad

Answer 2

@@ identifies a class variable.