Poltergeist (computer programming)

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 at the 1996 Object World West Conference:^{[ citation needed ]}

As a 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.

A poltergeist can often be identified by its name; they often include words such as "Manager", "Controller", "Supervisor", "StartProcess", etc. in the name.

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 pattern.

To remove a poltergeist, delete the class and insert its functionality in the invoked class, possibly by inheritance or as a mixin.

There have been proposed methods in detecting poltergeists in code for refactoring. ^[1]

Example

This Poltergeist class in this C++ example can be seen as a "poltergeist object", due to not adding additional functionality or encapsulation and only increasing complexity with unnecessary abstraction.

importstd;usingString=std::string;// Poltergeist class that just holds a pointer, but adds no meaningful behaviorclassPoltergeist{private:String*s;// pointer to string, but the class itself doesn't do anything usefulpublic:explicitPoltergeist(String*s):s{s}{}~Poltergeist(){deletestr;}[[nodiscard]]Stringget()constnoexcept{returns;}// No additional behavior or meaningful functionality};intmain(){// Create a Poltergeist object that just holds a pointer to the stringPoltergeistp(newString("Hello, world!"));// Just passes the data around without adding valuestd::println(*p.get());return0;}

This could instead be more appropriately done using a smart pointer.

importstd;usingString=std::string;template<typenameT>usingUniquePtr=std::unique_ptr<T>;// Use smart pointers directly to manage memoryUniquePtr<String>s=std::make_unique<String>("Hello, World!");std::println(*s);

See also

• Anti-pattern
• Factory (object-oriented programming)
• YAGNI principle

References

1. Al-Rubaye, Samer Raad Azzawi; Selcuk, Yunus Emre (24–26 November 2017). "An investigation of code cycles and Poltergeist anti-pattern". 2017 8th IEEE International Conference on Software Engineering and Service Science (ICSESS). pp. 139–140. doi:10.1109/ICSESS.2017.8342882. ISBN   978-1-5386-0497-7.

• Brown, William J. (1998). "Chapter 5: Software Development AntiPatterns". AntiPatterns: Refactoring Software, Architectures, and Projects in Crisis . New York, USA: John Wiley & Sons. ISBN   0-471-19713-0.

External links

• Development AntiPatterns