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In object-oriented programming OOPa factory is an object for creating other objects — formally a factory is a function or method that returns objects of a varying prototype or class [1] from some method call, which is assumed to be "new". This is a basic concept in OOP, and forms the basis bitcoin php class construct a number of related software design patterns.
In class-based programminga 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 bitcoin php class construct process class instantiationwhile 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 bitcoin php class construct to create objects by being clonedwhile a factory can create objects by cloning various prototypes, or by other bitcoin php class construct schemes. Factories may be invoked in various ways, most often a method call a factory methodsometimes by being called as a function if the factory is a function object a factory function. In some languages factories are generalizations of constructors, meaning constructors bitcoin php class construct themselves factories and these are invoked in the same way.
In other languages factories and constructors are invoked differently, for example using the keyword new to invoke constructors but an ordinary method call to invoke factories; in these languages factories are an abstraction of constructors but not strictly a generalization, as constructors are not themselves factories. Terminology differs as to whether the concept of a factory is itself a design pattern — in the seminal book 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[2] [3] while bitcoin php class construct consider the concept itself a programming idiom[4] reserving the term "factory pattern" or "factory patterns" to bitcoin php class construct 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.
OOP provides polymorphism on object use by method dispatchformally subtype polymorphism via single dispatch determined by the type of the object on which the method is called. However, this does not work for constructors, as constructors create an object of some type, rather than use an existing object.
More concretely, when a constructor is called, there is no object yet on which to dispatch. Using factories instead of constructors or prototypes allows one to use polymorphism for object creation, not only object use. Specifically, using factories provides encapsulationand means the code is not tied to specific classes or objects, and thus the class hierarchy or prototypes can be changed or refactored without needing to change code that uses them — they abstract from the class hierarchy or prototypes.
More technically, in languages where factories generalize constructors, factories can usually be used anywhere constructors can be, [c] meaning that interfaces that accept a constructor can also in general accept a factory — usually one only need something that creates an object, rather than needing to specify a class and instantiation. For example, in Python, the collections. The factory is passed as an argument to the constructor, and can itself be a constructor, or any thing that bitcoin php class construct like a constructor — a callable object that returns an object, i.
For example, using the list constructor for lists:. Factory objects are used in situations where getting hold of an object of a particular kind is a more complex process than simply creating a new object, notably if complex allocation or initialization is desired. Bitcoin php class construct of the processes required in the creation of an object include determining which object to create, managing the lifetime of the object, and managing specialized build-up and tear-down concerns of the object.
The factory object might decide to create the object's class if applicable dynamically, return it from bitcoin php class construct object poolbitcoin php class construct complex configuration on the object, or other things. Similarly, using this definition, a singleton implemented by the singleton pattern is a formal factory — it returns an object, but does not create new objects beyond the single instance. The simplest example bitcoin php class construct a factory is a simple factory function, which just invokes a constructor and returns the result.
In Python, a factory function f that instantiates a class A can be implemented as:. Factories may be invoked in various ways, most often a method call a factory methodsometimes by being called as a function if the factory is a callable object a factory function. In some languages constructors and factories have identical syntax, while in others constructors have special syntax. In languages where constructors and factories have identical syntax, like Python, Perl, Ruby, Object Pascal, and F[e] constructors can be transparently replaced by factories.
In languages where they differ, one must distinguish them in interfaces, and switching between constructors and factories requires changing the calls. In languages where objects are dynamically allocatedas in Java or Python, factories are semantically equivalent to constructors. If a constructor can be passed as an argument to a function, then invocation of the constructor and allocation of the return value must be done dynamically at run time, and thus have similar or identical semantics to invoking a factory.
Factories are used in various design patternsspecifically in creational patterns such as the Design pattern object library. Specific recipes have been developed to implement them in many languages. For example, several " GoF patterns ", like the " Factory method pattern ", the " Builder " or even the " Singleton " are implementations of this concept.
The " Abstract factory pattern " instead is a method to build collections of factories. In some design patterns, a factory object has a method for every kind of object it is capable of creating. These methods optionally accept parameters defining how the object is created, bitcoin php class construct then return the created object.
Factory objects are common in toolkits and frameworks where library code needs to create objects of types which bitcoin php class construct be subclassed by applications using the bitcoin php class construct. They are also used in test-driven development to allow classes to be put under test.
Bitcoin php class construct determine the actual concrete bitcoin php class construct of object to be created, and it is here that the object is actually created. As the factory only returns an abstract interface to the object, the client code does not know — and is not burdened by — the actual concrete type of the object which was just created.
However, the type of a concrete object is known by the abstract factory. In particular, this means:. Factories, specifically factory methods, are common in toolkits and frameworkswhere library code needs to create objects of types that may be subclassed by applications using the framework.
Parallel class hierarchies often require objects from one hierarchy to be able to create appropriate objects from another. Factory methods are used in test-driven development to allow classes to be put under test. For testing, TestFoo a subclass of Foo is then bitcoin php class construct, with the virtual factory method createDangerous overridden to create and return FakeDangerousa fake object.
Unit tests then use TestFoo to test the functionality of Foo without incurring the side effect of using a real Dangerous object. Besides use in design patterns, factories, especially factory methods, have various benefits and variations. A factory method has a distinct name. In many object-oriented languages, constructors must have the same name as the class they are in, which can lead to ambiguity if there is more than one way bitcoin php class construct create an object see overloading.
Factory methods have no such constraint and can have descriptive names; these are sometimes known as alternative constructors. As an example, when complex numbers are created from two real numbers the real numbers can be interpreted as Cartesian or polar coordinates, but using factory methods, the meaning is clear, as illustrated by the following example in C.
When factory methods are used for disambiguation like this, the raw constructors are often made private to force clients to use the factory methods. Factory methods encapsulate the creation of objects. This can be useful if the creation process is very complex; for example, if it depends on settings in configuration files or on user input. Consider as an example a program that reads image files.
The program supports different image formats, represented by a reader class for each format. Each time the program reads an image, it needs to create a reader of the appropriate type based on some information in the file.
This logic can be encapsulated in a factory method. This approach has also been referred to as the Simple Factory. There are three limitations associated with the use of the factory method. The first relates to refactoring existing code; the other two relate to extending a class. All three problems could be alleviated by altering the underlying programming language to make factories first-class class members bitcoin php class construct also Virtual class.
From Wikipedia, the free encyclopedia. For the Bitcoin php class construct design patterns using factories, see factory method pattern and abstract factory pattern. FromPolar 1Math. In other languages there is a sharp distinction between constructors and methods. Baking with OO Goodness: Working Effectively with Legacy Code. Upper Saddle River, NJ: Prentice Hall Professional Technical Reference. Vancouver, British Columbia, Canada: Head First Design Patterns. Retrieved from " https: Views Bitcoin php class construct Edit View history.
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