No means to access outer class from singleton class.

gistfile1.rb

# Doesn't work; needs reference to outer class object.
class SomeClass
  class << self
    extend Delegate
    
    def hash
      @hash ||= {}
    end
    
    delegate hash, :[]=, :has_key?, :each
  end
end

# Works because everything is done in the outer class object.
class SomeClass
  class << self
    def hash
      @hash ||= {}
    end
  end
  
  extend Delegate
  delegate hash, :[]=, :has_key?, :each
end