Duck typing

gistfile1.rb

class Duck
 def quack
   "Quack quack"
 end
end

class Person
  def quack
    "Bad impression of Donald Duck"
  end
end

things = []
things << Person.new
things << Duck.new

things.each { |v| puts "#{v} says #{v.quack}" }

Output

#<Person:0x007fb8f3162110> says Bad impression of Donald Duck
#<Duck:0x007fb8f31620e8> says Quack quack