Another option is to use the +(void)initialize method. From the documentation: The runtime sends initialize to each class in a program exactly one time just before the class, or any class that inherits from it, is sent its first message from within the program. (Thus the method may never be invoked if the class is … Read more
This is a perfectly acceptable and thread-safe way to create an instance of your class. It may not technically be a “singleton” (in that there can only ever be 1 of these objects), but as long as you only use the [Foo sharedFoo] method to access the object, this is good enough.
I very much disagree with Dianne Hackborn’s response. We are bit by bit removing all singletons from our project in favor of lightweight, task scoped objects which can easiliy be re-created when you actually need them. Singletons are a nightmare for testing and, if lazily initialized, will introduce “state indeterminism” with subtle side effects (which … Read more
Thanks to Dart’s factory constructors, it’s easy to build a singleton: class Singleton { static final Singleton _singleton = Singleton._internal(); factory Singleton() { return _singleton; } Singleton._internal(); } You can construct it like this main() { var s1 = Singleton(); var s2 = Singleton(); print(identical(s1, s2)); // true print(s1 == s2); // true }
I think the easiest way is to declare a simple object literal: var myInstance = { method1: function () { // … }, method2: function () { // … } }; If you want private members on your singleton instance, you can do something like this: var myInstance = (function() { var privateVar=””; function privateMethod … Read more
I don’t really see the need, as a module with functions (and not a class) would serve well as a singleton. All its variables would be bound to the module, which could not be instantiated repeatedly anyway. If you do wish to use a class, there is no way of creating private classes or private … Read more
On my quest for the truth I discovered that there are actually very few “acceptable” reasons to use a Singleton. One reason that tends to come up over and over again on the internets is that of a “logging” class (which you mentioned). In this case, a Singleton can be used instead of a single … Read more
tl;dr: Use the class constant approach if you are using Swift 1.2 or above and the nested struct approach if you need to support earlier versions. From my experience with Swift there are three approaches to implement the Singleton pattern that support lazy initialization and thread safety. Class constant class Singleton { static let sharedInstance … Read more
I wrote this answer back in ’09 when Android was relatively new, and there were many not well established areas in Android development. I have added a long addendum at the bottom of this post, addressing some criticism, and detailing a philosophical disagreement I have with the use of Singletons rather than subclassing Application. Read … Read more
Use an enum: public enum Foo { INSTANCE; } Joshua Bloch explained this approach in his Effective Java Reloaded talk at Google I/O 2008: link to video. Also see slides 30-32 of his presentation (effective_java_reloaded.pdf): The Right Way to Implement a Serializable Singleton public enum Elvis { INSTANCE; private final String[] favoriteSongs = { “Hound … Read more