metaprog.rb

class Picapau
  def voa
    p 'estou voando'
  end
end
 
woody = Picapau.new
amigo = Picapau.new
 
woody.voa # => estou voando
amigo.voa # => estou voando
 
def woody.rir
  "hehehehe-hehehehe-hehehehehehe"
end
 
p woody.rir # => hehehehe-hehehehe-hehehehehehe
# p amigo.rir # => NoMethodError: undefined method ‘rir’ for ...
 
p woody.class # => Picapau
p amigo.class # => Picapau
 
p woody.class == amigo.class # => true
 
p woody.methods - amigo.methods # => ["rir"]
 
p woody.singleton_methods # => ["rir"]
p amigo.singleton_methods # => []
 
class Object
    def singleton_class
      class << self
        self
      end
    end
end
 
p woody.singleton_class # => Class:Picapau:0x...
p amigo.singleton_class # => Class:Picapau:0x...(diferente)
p woody.singleton_class == amigo.singleton_class # => false
 
 
class ARBase
  def self.belongs_to
    def leo
      p 'leo'
    end
  end
   
end
 
class B < ARBase
  belongs_to
end
 
B.new.leo # => leo