How do you do polymorphism in Ruby?

Question

In C#, I can do this:

class Program
{
    static void Main(string[] args)
    {
        List<Animal> animals = new List<Animal>();

        animals.Add(new Dog());
        animals.Add(new Cat());

        foreach (Animal a in animals)
        {
            Console.WriteLine(a.MakeNoise());
            a.Sleep();
        }
    }
}

public class Animal
{
    public virtual string MakeNoise() { return String.Empty; }
    public void Sleep()
    {
        Console.Writeline(this.GetType().ToString() + " is sleeping.");
    }
}

public class Dog : Animal
{
    public override string MakeNoise()
    {
        return "Woof!";
    }
}

public class Cat : Animal
{
    public override string MakeNoise()
    {
        return "Meow!";
    }
}

Obviously, the output is (Slightly paraphrased):

• Woof
• Dog is Sleeping
• Meow
• Cat is Sleeping

Since C# is often mocked for its verbose type syntax, how do you handle polymorphism/virtual methods in a duck typed language such as Ruby?

Answer 1

All the answers so far look pretty good to me. I thought I'd just mention that the whole inheritance thing is not entirely necessary. Excluding the "sleep" behaviour for a moment, we can achieve the whole desired outcome using duck-typing and omitting the need to create an Animal base class at all. Googling for "duck-typing" should yield any number of explanations, so for here let's just say "if it walks like a duck and quacks like a duck..."

The "sleep" behaviour could be provided by using a mixin module, like Array, Hash and other Ruby built-in classes inclue Enumerable. I'm not suggesting it's necessarily better, just a different and perhaps more idiomatically Ruby way of doing it.

module Animal
  def sleep
    puts self.class.name + " sleeps"
  end
end

class Dog
  include Animal
  def make_noise
    puts "Woof"
  end
end

class Cat
  include Animal
  def make_noise
    puts "Meow"
  end
end

You know the rest...

Answer 2

edit: added more code for your updated question

disclaimer: I haven't used Ruby in a year or so, and don't have it installed on this machine, so the syntax might be entirely wrong. But the concepts are correct.

---

The exact same way, with classes and overridden methods:

class Animal
    def MakeNoise
        return ""
    end
    def Sleep
        print self.class.name + " is sleeping.\n"
    end
end

class Dog < Animal
    def MakeNoise
        return "Woof!"
    end
end

class Cat < Animal
    def MakeNoise
        return "Meow!"
    end
end

animals = [Dog.new, Cat.new]
animals.each {|a|
    print a.MakeNoise + "\n"
    a.Sleep
}