make all Ruby things Enumerable

object_enumerable.rb

class Object
  def each(&block)
    return to_enum(:each) { 1 } unless block
    [self].each(&block)
  end
  include Enumerable
end

class NilClass
  def each(&block)
    return to_enum(:each) { 0 } unless block
  end
end

#---

def greetings(users)
  users.map { |user| "Hello, #{user}" }
end

greetings %w(Finn Jake) #=> ["Hello, Finn", "Hello, Jake"] 
greetings 'Finn'        #=> ["Hello, Finn"]
greetings nil           #=> nil