The best way to implement the Singleton pattern in Java and Ruby

I haven’t posted anything lately, but I just received my brand new Das Keyboard and now I simply can’t stop typing. Recently I’ve been going through some effective techniques to implement popular design patterns and I was surprised to see how few people were aware of them. For example since Java 5 the best way to implement the Singleton pattern is simply to use an enum like this:

public enum SomeClass {
    INSTANCE;
}

This is possible due to the fact that in Java (unlike in C++ and C#) enums are full-blown classes (although they do not support features like inheritance for example). You get an added bonus when using an enum class – you do not have to worry about serialization – this is handled for you behind the scenes.

And this is how one should implement the Singleton pattern in Ruby:

require 'singleton'

class Some
  include Singleton
end

Through the magic of Ruby’s mix-ins you get a private constructor for your class and an instance method with which you can obtain a reference to the single instance of the class. And best of all – because this library has undergone a substantial degree of testing it is pretty much bulletproof. Things hardly get simpler than that.