A Safari for Deviating GoF Pattern Definitions and Examples on the Web.

The Gang of Four (GoF) patterns have been around for many years now. People use them to solve object-oriented design problems. The main source to consult for the GoF patterns is the seminal book published by Gamma, Helm, Johnson, and Vlissides in 1994. However, today there is also a large amount of information about the GoF patterns on the Web. There, the developers can find pattern definitions and code examples. In this paper, we assess the compliance of pattern definitions and examples found on the Web to the original GoF pattern definitions. We study a corpus of definitions and examples, gathered from 4 well-known sites. According to our findings, most of the provided pattern definitions comply with the original GoF pattern definitions. However, there are some intent deviations that result in incorrect definitions. There are also a few deviations that concern missing and incomplete participants. When it comes to the patterns examples, the situation is quite different. Deviations in the examples are much more frequent and include missing participants, incomplete participants, and erroneous participants. The paper concludes with a discussion of the practical implications of our findings for the developers.