Poltergeist (computer programming): Difference between revisions

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{{Short description|Computer programming object}}

In [[computer programming]], a '''poltergeist''', (or '''gypsy wagon''',) is a short -lived, typically [[State (computer science)|stateless]] object used to perform initialization or to invoke methods in otheranother, more permanent class. It is considered an [[anti-pattern]]. The original definition is by Michael Akroyd at the 1996 Object World West Conference:{{cn|date=October 2024}}

{{blockquote|As a [[Vardo (Romani wagon)|gypsy wagon]] or a [[poltergeist]] 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 anti-pattern is poor object design.<!-- I think this is a quote -->}}

A poltergeist can often be identified by its name; they are often called "manager_", "controller_", "supervisor", "start_process", etc.

A '''poltergeist''' is an example of an [[anti-pattern]].

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.

The original definition is by Michael Akroyd 1996 - Object World West Conference.

Poltergeists should not be confused with long-lived, state-bearing objects of a [[Software design pattern|pattern]] such as [[model–view–controller]], or tier-separating patterns such as [[business delegate pattern]].

As a gypsy wagon or a poltergeist appear and disappear mysteriously so is 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.

Gypsy wagon can be identified also by their name.

Typically these are stateless "supervision" classes, used only to call methods of other classes, so several time are called "manager_" , "controller_", "start_process", etc..

To remove a Gypsy Wagonpoltergeist, delete the class and insert its functionality in the invoked class, possibly by [[Inheritance (object-oriented programming)|inheritance]] or as a [[mixin]].

functionality in the invoked class.

There have been proposed methods in detecting poltergeists in code for refactoring.<ref>{{cite book |last1=Al-Rubaye |first1=Samer Raad Azzawi |last2=Selcuk |first2=Yunus Emre |title=2017 8th IEEE International Conference on Software Engineering and Service Science (ICSESS) |chapter=An investigation of code cycles and Poltergeist anti-pattern |date=24–26 November 2017 |pages=139–140 |doi=10.1109/ICSESS.2017.8342882 |isbn=978-1-5386-0497-7 |chapter-url=https://ieeexplore.ieee.org/document/8342882/authors#authors}}</ref>

==See also==

* [[Anti-pattern]]

* [[Factory (object-oriented programming)]]

* [[YAGNI|YAGNI principle]]

==References==

<references/>

*{{cite book |last=Brown |first=William J. |title=AntiPatterns: Refactoring Software, Architectures, and Projects in Crisis |year=1998 |publisher=John Wiley & Sons |___location=New York, USA |isbn=0-471-19713-0 |chapter=Chapter 5: Software Development AntiPatterns |url-access=registration |url=https://archive.org/details/antipatternsrefa0000unse }}

==External links==

* [http://www.antipatterns.com/dev_cat.htm Development AntiPatterns]

[[Category:Anti-patterns]]

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