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What Is a Metaclass?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 11 November 2016
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    Conjecture Corporation
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A metaclass is used in object oriented programming (OOP) and is typically thought of as a classes' class. Like most meta information, the metaclass works behind the program and is never seen by the user. A metaclass is able to modify information from the class and can be linked to one or many classes, depending on the coding structure. Not all OOP structures include metaobject coding, and some might only offer metaobject coding in advanced formats.

In nearly all types of coding, meta coding is a tag or line of code that works on the program, but it is not overtly seen by the user. Meta information is above the code and is able to modify pieces of information or add to the program without directly interfering with the program. In OOP, a metaclass is used to take a class and modify its behavior.

A class in OOP is a set of instances or objects placed under one umbrella term. For example, the programmer can create a class called “House.” Under this, the programmer creates objects that modify or reproduce aspects commonly found in a house, such as rooms, furniture and people. While a class is able to modify these objects, a metaclass would work on modifying the class itself.

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Classes in OOP are typically dynamic and may undergo many changes before the program is finished. Metaclasses are static pieces of information that rarely change unless the programmer finds the meta information is not working correctly. This keeps metaclasses from accidentally working with volatile data and also ensures the behavior modifiers cannot be manipulated.

Depending on the need of the programmer, a metaclass will either be linked to a single class or to many classes at once. Programmers most often connect the metaclass to one class and add unique rules or behaviors into the metaobject coding. If there are several classes that can all undergo the same behavior modification, the meta information will be applied to several different classes. This is possible because the metaobject coding is titled and can be easily called whenever needed.

While this is a common occurrence in intermediate to advanced programs, some OOP structures do not offer metaclasses. This is either because there is no need for them or there are other objects or classes that have similar functions but are called something else. Some coding structures may also offer only complex and advanced metaclasses, where others have simpler ones for intermediate coders to use.

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