Don't repeat yourself

From Wikipedia, the free encyclopedia
Jump to: navigation, search

In software engineering, don’t repeat yourself (DRY) is a principle of software development, aimed at reducing repetition of information of all kinds, especially useful in multi-tier architectures. The DRY principle is stated as “Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.” The principle has been formulated by Andy Hunt and Dave Thomas in their book The Pragmatic Programmer. They apply it quite broadly to include “database schemas, test plans, the build system, even documentation.”[1] When the DRY principle is applied successfully, a modification of any single element of a system does not require a change in other logically unrelated elements. Additionally, elements that are logically related all change predictably and uniformly, and are thus kept in sync. Besides using methods and subroutines in their code, Thomas and Hunt rely on code generators, automatic build systems, and scripting languages to observe the DRY principle across layers.

DRY vs WET solutions[edit]

Violations of DRY are typically referred to as WET solutions, which is commonly taken to stand for either “write everything twice” or “we enjoy typing”.[2][3]

See also[edit]


  1. ^ Dave Thomas, interviewed by Bill Venners (2003-10-10). "Orthogonality and the DRY Principle". Retrieved 2006-12-01. 
  2. ^ Justin Lee (2006-03-08). "DRY is for losers". Retrieved 2013-08-31. 
  3. ^ Alex Papadimoulis (2011-12-08). "The WET Cart". Retrieved 2012-05-21. 

External links[edit]