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In software engineering, the initialization-on-demand holder (design pattern) idiom is a lazy-loaded singleton. In all versions of Java, the idiom enables a safe, highly concurrent lazy initialization of static fields with good performance. [1] [2]
Complete article "Java Singleton Pattern Explained" Four different ways to implement singleton in Java "Ways to implement singleton in Java" Book extract: Implementing the Singleton Pattern in C# by Jon Skeet; Singleton at Microsoft patterns & practices Developer Center; IBM article "Double-checked locking and the Singleton pattern" by Peter Haggar
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.
In Java, the multiton pattern can be implemented using an enumerated type, with the values of the type corresponding to the instances. In the case of an enumerated type with a single value, this gives the singleton pattern. In C#, we can also use enums, as the following example shows:
The object pool pattern is a software creational design pattern that uses a set of initialized objects kept ready to use – a "pool" – rather than allocating and destroying them on demand.
The second notable difference is that the void type is special and can never be stored in a record type, i.e. in a struct or a class in C/C++. In contrast, the unit type can be stored in records in functional programming languages, i.e. it can appear as the type of a field; the above implementation of the unit type in C++ can also be stored.
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.
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.