Poltergeist (computer programming)

In computer programming, a poltergeist 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:
A poltergeist can often be identified by its name; they often include words such as "", "", "", "", 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.

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.

import std;
using String = std::string;
// Poltergeist class that just holds a pointer, but adds no meaningful behavior
class Poltergeist ;
int main

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

import std;
using String = std::string;
template
using UniquePtr = std::unique_ptr;
// Use smart pointers directly to manage memory
UniquePtr s = std::make_unique;
std::println;

Another example of a poltergeist/gypsy wagon object, is the following, where UserCreator is instantiated just to perform some basic actions.

import std;
using String = std::string;
class UserManager ;
// The poltergeist class
class UserCreator ;
int main

This could be more appropriately done like so, avoiding any poltergeist class entirely:

// Avoid the UserCreator poltergeist entirely
int main