some ruby meta programming demo.

eigenclass.rb

#Person
class Person
end

#class method
class Person
  def self.address
    puts "hangzhou"
  end
end

Person.address


#eigenclass
class Person
  class << self
    def name
      puts "saito"
    end
  end
end

Person.name

#===============================#

#another herpderp eigenclass demo

li = Person.new
zh = Person.new

class << zh
  def kick_li
    puts "kick li"
  end
end

zh.kick_li
#li.kick_li  #=>will got a NoMethodError

#===============================#

#class method
Person.instance_eval do
  def age
    puts "22"
  end
end

Person.age

#instance method
Person.class_eval do
  def sex
    puts "male"
  end
end

Person.new.sex

#Class method
def Person.nick
  puts "s"
end

Person.nick

#open Person Class
class << Person
  def species
    puts "chinese"
  end
end

Person.species

#le herpderp Class method (MAP
class Class
  def loud_name
    puts "Saito"
  end
end

Person.loud_name