Generation gap is a software design pattern documented by John Vlissides that treats automatically generated code differently than code that was written by a developer. Modifications should not be made to generated code, as they would be overwritten if the code generation process was ever re-run, such as during recompilation. Vlissides proposed creating a subclass of the generated code which contains the desired modification. This might be considered an example of the template method pattern.
Modern languages
Modern byte-code language like Java were in their early stages when Vlissides developed his ideas. In a language like Java or C#, this pattern may be followed by generating an interface, which is a completely abstract class. The developer would then hand-modify a concrete implementation of the generated interface.
References
Fowler, Martin. "Generation Gap". martinfowler.com/. Retrieved 9 August 2014. http://martinfowler.com/dslCatalog/generationGap.html ↩
Vlissides, John (1998-06-22). Pattern Hatching: Design Patterns Applied. Addison-Wesley Professional. pp. 85–101. ISBN 978-0201432930. 978-0201432930 ↩