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In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns , which describe how to solve recurring problems in object-oriented software. [ 1 ]
This pattern can be implemented in several ways depending on the host programming language, such as the singleton design pattern, object-oriented static members in a class and procedural global functions. In Python, the pattern is built into the language, and each .py file is automatically a module.
If the helper object is static (one per class loader), an alternative is the initialization-on-demand holder idiom [11] (See Listing 16.6 [12] from the previously cited text.) // Correct lazy initialization in Java class Foo { private static class HelperHolder { public static final Helper helper = new Helper (); } public static Helper getHelper ...
In computer programming, lazy initialization is the tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns.The book was written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, with a foreword by Grady Booch.
Some use cases for this pattern are static polymorphism and other metaprogramming techniques such as those described by Andrei Alexandrescu in Modern C++ Design. [7] It also figures prominently in the C++ implementation of the Data, Context, and Interaction paradigm. [8]
CLASS-ID. name« INHERITS« FROM» parentclasses». FACTORY« IMPLEMENTS interfaces». class-members. END FACTORY. OBJECT« IMPLEMENTS interfaces». instance-members. END OBJECT. END CLASS name. INTERFACE-ID. name« INHERITS« FROM» interfaces». members. END INTERFACE name. — Cobra class name «inherits parentclass» «implements interfaces ...