In exactly the same way that you (should) have been doing it already: + (instancetype)sharedInstance { static MyClass *sharedInstance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ sharedInstance = [[MyClass alloc] init]; // Do any other initialisation stuff here }); return sharedInstance; }
Since TS 2.0, we have the ability to define visibility modifiers on constructors, so now we can do singletons in TypeScript just like we are used to from other languages. Example given: class MyClass { private static _instance: MyClass; private constructor() { //… } public static get Instance() { // Do you need arguments? Make … Read more
A singleton is a class which only allows one instance of itself to be created – and gives simple, easy access to said instance. The singleton premise is a pattern across software development. There is a C# implementation “Implementing the Singleton Pattern in C#” covering most of what you need to know – including some … Read more
/** * Singleton class * */ final class UserFactory { private static $inst = null; // Prevent cloning and de-serializing private function __clone(){} private function __wakeup(){} /** * Call this method to get singleton * * @return UserFactory */ public static function Instance() { if ($inst === null) { $inst = new UserFactory(); } return … Read more
This, public enum MySingleton { INSTANCE; } has an implicit empty constructor. Make it explicit instead, public enum MySingleton { INSTANCE; private MySingleton() { System.out.println(“Here”); } } If you then added another class with a main() method like public static void main(String[] args) { System.out.println(MySingleton.INSTANCE); } You would see Here INSTANCE enum fields are compile … Read more
No, this is nothing to do with closures. A nested class has access to its outer class’s private members, including the private constructor here. Read my article on beforefieldinit. You may or may not want the no-op static constructor – it depends on what laziness guarantees you need. You should be aware that .NET 4 … Read more
Static constructors are guaranteed to be run only once per application domain, before any instances of a class are created or any static members are accessed. https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-constructors The implementation shown is thread safe for the initial construction, that is, no locking or null testing is required for constructing the Singleton object. However, this does not … Read more
Here is what is going on. First, the only global variables Python really has are module-scoped variables. You cannot make a variable that is truly global; all you can do is make a variable in a particular scope. (If you make a variable inside the Python interpreter, and then import other modules, your variable is … Read more
dispatch_once() is absolutely synchronous. Not all GCD methods do things asynchronously (case in point, dispatch_sync() is synchronous). The use of dispatch_once() replaces the following idiom: + (MyClass *)sharedInstance { static MyClass *sharedInstance = nil; @synchronized(self) { if (sharedInstance == nil) { sharedInstance = [[MyClass alloc] init]; } } return sharedInstance; } The benefit of dispatch_once() … Read more
Answer: Use a Singleton if: You need to have one and only one object of a type in system Do not use a Singleton if: You want to save memory You want to try something new You want to show off how much you know Because everyone else is doing it (See cargo cult programmer … Read more