ruby constant lookup

a.rb

module A
  class << self
    def foo
      p B
    end
  end

  B = "A::B"
end

B = "Toplevel B"

A.foo # => "A::B"

b.rb

module A
  B = "A::B"
end

def A.foo
  p B
end

B = "Toplevel B"

A.foo # => "Toplevel B"