Poltergeist (computer science)
Encyclopedia
In computer programming
, a poltergeist (or gypsy wagon) is a short-lived, typically stateless object used to perform initialization or to invoke methods in another, more permanent class. It is considered an anti-pattern
. The original definition is by Michael Akroyd 1996 - Object World West Conference:
A poltergeist can often be identified by its name; they are often called "manager_", "controller_", "start_process", etc.
Sometimes, poltergeist classes are created because the programmer anticipated the need for a more complex architecture. For example, a poltergeist arises if the same method acts as both the client and invoker in a Command pattern
, and the programmer anticipates separating the two phases. However, this more complex architecture may actually never materialize.
Poltergeists should not be confused with long-lived, state-bearing objects of a pattern
such as Model-view-controller
, or tier-separating patterns such as Business-Delegate.
To remove a poltergeist, delete the class and insert its functionality in the invoked class, possibly by inheritance
or as a mixin
.
Computer programming
Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...
, a poltergeist (or gypsy wagon) is a short-lived, typically stateless object used to perform initialization or to invoke methods in another, more permanent class. It is considered an anti-pattern
Anti-pattern
In software engineering, an anti-pattern is a pattern that may be commonly used but is ineffective and/or counterproductive in practice.The term was coined in 1995 by Andrew Koenig,...
. The original definition is by Michael Akroyd 1996 - Object World West Conference:
- "As a gypsy wagon or a poltergeistPoltergeistA poltergeist is a paranormal phenomenon which consists of events alluding to the manifestation of an imperceptible entity. Such manifestation typically includes inanimate objects moving or being thrown about, sentient noises and, on some occasions, physical attacks on those witnessing the...
appears and disappears mysteriously, so does this short lived object. As a consequence the code is more difficult to maintain and there is unnecessary resource waste. The typical cause for this antipattern is poor object design."
A poltergeist can often be identified by its name; they are often called "manager_", "controller_", "start_process", etc.
Sometimes, poltergeist classes are created because the programmer anticipated the need for a more complex architecture. For example, a poltergeist arises if the same method acts as both the client and invoker in a Command pattern
Command pattern
In object-oriented programming, the command pattern is a design pattern in which an object is used to represent and encapsulate all the information needed to call a method at a later time...
, and the programmer anticipates separating the two phases. However, this more complex architecture may actually never materialize.
Poltergeists should not be confused with long-lived, state-bearing objects of a pattern
Pattern
A pattern, from the French patron, is a type of theme of recurring events or objects, sometimes referred to as elements of a set of objects.These elements repeat in a predictable manner...
such as Model-view-controller
Model-view-controller
Model–view–controller is a software architecture, currently considered an architectural pattern used in software engineering. The pattern isolates "domain logic" from the user interface , permitting independent development, testing and maintenance of each .Model View Controller...
, or tier-separating patterns such as Business-Delegate.
To remove a poltergeist, delete the class and insert its functionality in the invoked class, possibly by inheritance
Inheritance (computer science)
In object-oriented programming , inheritance is a way to reuse code of existing objects, establish a subtype from an existing object, or both, depending upon programming language support...
or as a mixin
Mixin
In object-oriented programming languages, a mixin is a class that provides a certain functionality to be inherited or just reused by a subclass, while not meant for instantiation , Mixins are synonymous functionally with abstract base classes...
.