InheritanceAndMethodParametersInCrystal.cr

abstract class Animal
  abstract def speak
end

class Dog < Animal
  def speak
    "Bark!"
  end
end

class Cat < Animal
  def speak
    "Meow!"
  end
end

def printSpeak(animal : Animal)
  puts animal.speak
end

dog = Dog.new
cat = Cat.new

printSpeak(cat)