factory

In object-oriented programming, a factory is an object for creating other objects; formally, it is a function or method that returns objects of a varying prototype or class from some method call, which is assumed to be "new". More broadly, a subroutine that returns a "new" object may be referred to as a "factory", as in factory method or factory function. The factory pattern is the basis for a number of related software design patterns. Motivation In class-based programming, a factory is an abstraction of a constructor of a class, while in prototype-based programming a factory is an abstraction of a prototype object. A constructor is concrete in that it creates objects as instances of a single class, and by a specified process (class instantiation), while a factory can create objects by instantiating various classes, or by using other allocation schemes such as an object pool. A prototype object is concrete in that it is used to create objects by being cloned, while a factory can create objects by cloning various prototypes, or by other allocation schemes. A factory may be implemented in various ways. Most often it is implemented as a method, in which case it is called a factory method. Sometimes it is implemented as a function, in which case it is called a factory function. In some languages, constructors are themselves factories. However, in most languages they are not, and constructors are invoked in a way that is idiomatic to the language, such as by using the keyword new, while a factory has no special status and is invoked via an ordinary method call or function call. In these languages, a factory is an abstraction of a constructor, but not strictly a generalization, as constructors are not themselves factories. Terminology Terminology differs as to whether the concept of a factory is itself a design pattern – in Design Patterns there is no "factory pattern", but instead two patterns (factory method pattern and abstract factory pattern) that use factories. Some sources refer to the concept as the factory pattern, while others consider the concept itself a programming idiom, reserving the term "factory pattern" or "factory patterns" to more complicated patterns that use factories, most often the factory method pattern; in this context, the concept of a factory itself may be referred to as a simple factory. In other contexts, particularly the Python language, "factory" itself is used, as in this article.