(1) UPDATE 2019: ES7 Version class Singleton { static instance; constructor() { if (instance) { return instance; } this.instance = this; } foo() { // … } } console.log(new Singleton() === new Singleton()); (2) ES6 Version class Singleton { constructor() { const instance = this.constructor.instance; if (instance) { return instance; } this.constructor.instance = this; } … Read more
Performing the lock is terribly expensive when compared to the simple pointer check instance != null. The pattern you see here is called double-checked locking. Its purpose is to avoid the expensive lock operation which is only going to be needed once (when the singleton is first accessed). The implementation is such because it also … Read more
Often, singletons are used to introduce some kind of global state to an application. (More often than really necessary, to be honest, but that’s a topic for another time.) However, there are a few corner cases where even a stateless singleton can be useful: You expect to extend it with state in the foreseeable future. … Read more
A singleton bean in Spring and the singleton pattern are quite different. Singleton pattern says that one and only one instance of a particular class will ever be created per classloader. The scope of a Spring singleton is described as “per container per bean”. It is the scope of bean definition to a single object … Read more
All of the above is overcomplicated. There is a school of thought which says design patterns are showing deficiencies of actual language. Languages with prototype-based OOP (classless) do not need a singleton pattern at all. You simply create a single(ton) object on the fly and then use it. As for modules in node, yes, by … Read more
The Google Testing blog has a series of entries about avoiding Singleton (in order to create testable code). Maybe this can help you: Using dependency injection to avoid singletons Singletons are Pathological Liars Root Cause of Singletons Where have all the Singletons Gone? The last article explains in detail how to move the creation of … Read more
Yes, it is necessary. There are several methods you can use to achieve thread safety with lazy initialization: Draconian synchronization: private static YourObject instance; public static synchronized YourObject getInstance() { if (instance == null) { instance = new YourObject(); } return instance; } This solution requires that every thread be synchronized when in reality only … Read more
Singletons have very little – if not to say no – use in PHP. In languages where objects live in shared memory, Singletons can be used to keep memory usage low. Instead of creating two objects, you reference an existing instance from the globally shared application memory. In PHP there is no such application memory. … Read more
readResolve is used for replacing the object read from the stream. The only use I’ve ever seen for this is enforcing singletons; when an object is read, replace it with the singleton instance. This ensures that nobody can create another instance by serializing and deserializing the singleton.
I’ll make my point very clear: a singleton with parameters is not a singleton. A singleton, by definition, is an object you want to be instantiated no more than once. If you are trying to feed parameters to the constructor, what is the point of the singleton? You have two options. If you want your … Read more