What is an anti-pattern?

Question

I am studying patterns and anti-patterns. I have a clear idea about patterns, but I don't get anti-patterns. Definitions from the web and Wikipedia confuse me a lot.

Can anybody explain to me in simple words what an anti-pattern is? What is the purpose? What do they do? Is it a bad thing or good thing?

Answer 1

Just like with a design pattern, an anti-pattern is also a template and a repeatable way of solving a certain problem, but in a non-optimal and ineffective way.

Answer 2

Anti-patterns are certain patterns in software development that are considered bad programming practices.

As opposed to design patterns which are common approaches to common problems which have been formalized and are generally considered a good development practice, anti-patterns are the opposite and are undesirable.

For example, in object-oriented programming, the idea is to separate the software into small pieces called objects. An anti-pattern in object-oriented programming is a God object which performs a lot of functions which would be better separated into different objects.

For example:

class GodObject {
    function PerformInitialization() {}
    function ReadFromFile() {}
    function WriteToFile() {}
    function DisplayToScreen() {}
    function PerformCalculation() {}
    function ValidateInput() {}
    // and so on... //
}

The example above has an object that does everything. In object-oriented programming, it would be preferable to have well-defined responsibilities for different objects to keep the code less coupled and ultimately more maintainable:

class FileInputOutput {
    function ReadFromFile() {}
    function WriteToFile() {}
}

class UserInputOutput {
    function DisplayToScreen() {}
    function ValidateInput() {}
}

class Logic {
    function PerformInitialization() {}
    function PerformCalculation() {}
}

The bottom line is there are good ways to develop software with commonly used patterns (design patterns), but there are also ways software is developed and implemented which can lead to problems. Patterns that are considered bad software development practices are anti-patterns.

Answer 3

An anti-pattern is the complement of a design pattern. An anti-pattern is a template solution you should not use in a certain situation.

Answer 4

Interestingly a given way of solving a problem can be both a pattern and an anti-pattern. Singleton is the prime example of this. It will appear in both sets of literature.

Answer 5

A pattern is an idea of how to solve a problem of some class. An anti-pattern is an idea of how not to solve it because implementing that idea would result in bad design.

An example: a "pattern" would be to use a function for code reuse, an "anti-pattern" would be to use copy-paste for the same. Both solve the same problem, but using a function usually leads to more readable and maintainable code than copy-paste.

Answer 6

Today, software engineering researchers and practitioners often use the terms “anti-pattern” and “smell” interchangeably. However, they are conceptually not the same. The Wikipedia entry of anti-pattern states that an anti-pattern is different from a bad practice or a bad idea by at least two factors. An anti-pattern is

"A commonly used process, structure or pattern of action that despite initially appearing to be an appropriate and effective response to a problem, typically has more bad consequences than beneficial results.”

It clearly indicates that an anti-pattern is chosen in the belief that it is a good solution (as a pattern) to the presented problem; however, it brings more liabilities than benefits. On the other hand, a smell is simply a bad practice that negatively affects the quality of a software system. For example, Singleton is an anti-pattern and God class (or Insufficient Modularization) is a design smell.