Editing Singleton pattern (section)

== Criticism ==
Some consider the singleton to be an [[anti-pattern]] that introduces [[global variables|global state]] into an application, often unnecessarily. This introduces a potential dependency on the singleton by other objects, requiring analysis of implementation details to determine whether a dependency actually exists.<ref name="google">{{cite web |title=Why Singletons Are Controversial |url=https://code.google.com/archive/p/google-singleton-detector/wikis/WhySingletonsAreControversial.wiki |archive-url=https://web.archive.org/web/20210506162753/https://code.google.com/archive/p/google-singleton-detector/wikis/WhySingletonsAreControversial.wiki |archive-date=6 May 2021 |access-date=28 August 2021 |website=Google Code Archive}}</ref> This increased [[Coupling (computer programming)|coupling]] can introduce difficulties with [[unit testing]].<ref name="button">{{cite news |last1=Button |first1=Brian |date=25 May 2004 |title=Why Singletons are Evil |work=Being Scott Densmore |publisher=Microsoft |url=https://docs.microsoft.com/en-us/archive/blogs/scottdensmore/why-singletons-are-evil |access-date=28 August 2021 |archive-url=https://web.archive.org/web/20210715184717/https://docs.microsoft.com/en-us/archive/blogs/scottdensmore/why-singletons-are-evil |archive-date=15 July 2021}}</ref> In turn, this places restrictions on any abstraction that uses the singleton, such as preventing [[Concurrency_(computer_science)|concurrent]] use of multiple instances.<ref name="button" /><ref>Steve Yegge. [http://steve.yegge.googlepages.com/singleton-considered-stupid Singletons considered stupid], September 2004</ref><ref name="googletesting.blogspot.com">Hevery, Miško, "[http://googletesting.blogspot.com/2008/11/clean-code-talks-global-state-and.html Global State and Singletons]", ''Clean Code Talks'', 21 November 2008.</ref>

Singletons also violate the [[single-responsibility principle]] because they are responsible for enforcing their own uniqueness along with performing their normal functions.<ref name="button" />