You Aren't Gonna Need It

"You aren't gonna need it" (YAGNI) is a principle which arose from extreme programming (XP) that states a programmer should not add functionality until deemed necessary. Other forms of the phrase include "You aren't going to need it" (YAGTNI) and "You ain't gonna need it" (YAGNI).

XP co-founder Ron Jeffries has written: "Always implement things when you actually need them, never when you just foresee that you need them." John Carmack has written "It is hard for less experienced developers to appreciate how rarely architecting for future requirements / applications turns out net-positive."

Context

YAGNI is a principle behind the XP practice of "do the simplest thing that could possibly work" (DTSTTCPW). It is meant to be used in combination with several other practices, such as continuous refactoring, continuous automated unit testing, and continuous integration. Used without continuous refactoring, it could lead to disorganized code and massive rework, known as technical debt. YAGNI's dependency on supporting practices is part of the original definition of XP.

See also

* Don't repeat yourself
* Feature creep
* If it ain't broke, don't fix it
* KISS principle
* Minimum viable product
* MoSCoW method
* Muntzing
* Overengineering
* Single-responsibility principle
* SOLID
* Unix philosophy
* Worse is better

References

{{Reflist, refs=

''Extreme Programming Installed'', Ronald E. Jeffries, Ann
Anderson, Chet Hendrickson, 2001, 265 pages, p. 190, webpage:

Books-Google-dIsC
quote:
"YAGNI: 'You Aren't Gonna Need It.' This slogan, one of XP's
most famous..., reminds us always to work on the story we have,
not something we think we're going to need."


''Extreme Programming examined'', Giancarlo Succi,
Michele Marchesi, 2001, 569 pages, webpage:

Books-Google-VSCh
quote:
"XP says 'do the simplest thing that could possibly work '
because 'you aren't gonna need it'."


{{cite book
, editor1=Lowell Lindstrom , editor2=Carmen Zannier , editor3=Erdogmus, Hakan
, title =Extreme Programming and Agile Methods – XP/Agile Universe 2004: 4th Conference on Extreme Programming and Agile Methods
, series=Lecture Notes in Computer Science , publisher=Springer
, location=Berlin , year=2004 , page=121 , isbn=3-540-22839-X


''Object-oriented & classical software engineering'',
Stephen R. Schach, 2007, 618 pages, p., webpage:

Book-Google-hWwh
quote:
"Two acronyms now associated with extreme programming are YAGNI
(you aren't gonna need it) and DTSTTCPW (do the simplest
thing that could possibly work)."


{{cite web
, url=http://ronjeffries.com/xprog/articles/practices/pracnotneed/
, title= You're NOT gonna need it!
, access-date=2007-11-07, date=April 4, 1998
, author=Ron Jeffries


Martin Fowler; Kent Beck (8 July 1999).
''Refactoring: Improving the Design of Existing Code''.
Addison-Wesley Professional, 431 pages, p. 68, webpage:

BGoogle-1M

{{ISBN, 978-0201485677. Quote:
"you aren't going to need it".


Mary Poppendieck; Tom Poppendieck (2003).
''Lean Software Development: An Agile Toolkit'', p.59, webpage:

BGoogle-hQ

Quote: "Kent Beck, ''Extreme Programming Explained'', Chapter
17, uses the acronym YAGNI (You Aren't Going to Need It) for this
practice and explains its rationale."


Russ Olsen (2007).
''Design Patterns in Ruby'', p.13, webpage:



{{ISBN, 9780321490452.
Quote: "This design principle comes out of the Extreme Programming
world and is elegantly summed up by the phrase You Ain't Gonna Need It (YAGNI
for short)."

Software development philosophies
Programming principles