Editing Singleton pattern (section)

{{Short description|Design pattern in object-oriented software development}}
[[File:Singleton UML class diagram.svg|thumb|A [[class diagram]] exemplifying the singleton pattern.]]

In [[object-oriented programming]], the '''singleton pattern''' is a [[software design pattern]] that restricts the [[Instantiation (computer science)|instantiation]] of a [[Class (computer programming)|class]] to a singular instance. It is one of the well-known [[Design Patterns|"Gang of Four" design patterns]], which describe how to solve recurring problems in object-oriented software.<ref name="GoF">{{cite book |author=Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides |url=https://archive.org/details/designpatternsel00gamm/page/127 |title=Design Patterns: Elements of Reusable Object-Oriented Software |publisher=Addison Wesley |year=1994 |isbn=0-201-63361-2 |pages=[https://archive.org/details/designpatternsel00gamm/page/127 127ff] |url-access=registration}}</ref> The pattern is useful when exactly one object is needed to coordinate actions across a system.

More specifically, the singleton pattern allows classes to:<ref>{{cite web |title=The Singleton design pattern - Problem, Solution, and Applicability |url=http://w3sdesign.com/?gr=c05&ugr=proble |access-date=2017-08-16 |website=w3sDesign.com}}</ref>
* Ensure they only have one instance
* Provide easy access to that instance
* Control their instantiation (for example, hiding the [[Constructor (object-oriented programming)|constructors]] of a [[Class (computer programming)|class]])

The term comes from the [[Singleton (mathematics)|mathematical concept of a singleton]].