How does the :: operator work in Ruby?

Question

I am new to Ruby and am confused by the :: operator. Why does the following code output 2, 3, 4, 5, 1 and not just output 1? Thanks!

class C
  a = 5
  module M
    a = 4
    module N
      a = 3
      class D
        a = 2
        def show_a
          a = 1
          puts a
        end
        puts a
      end
      puts a
    end
    puts a
  end
  puts a
end



d = C::M::N::D.new
d.show_a

Answer 1

If you remove the last line, you will see that you will get 5, 4, 3, 2. The reason is that the body of classes and modules is just regular code (unlike in some other languages). Therefore, those print statements will be executed when the classes/modules are getting parsed.

As to how :: works - it just lets you move around the scopes. ::A will reference the A in the main scope. Just A will refer to A in the current scope. A::B will refer to the B, that is inside the A, that is inside the current scope.