SOLID

This article is about the software concept. For the fundamental state of matter, see Solid. For other uses, see Solid (disambiguation).

In software engineering, SOLID is a mnemonic acronym for five design principles intended to make object-oriented designs more understandable, flexible, and maintainable. The principles are a subset of many principles promoted by American software engineer and instructor Robert C. Martin,^[1][2][3] first introduced in his 2000 paper Design Principles and Design Patterns discussing software rot.^{[2][4]: 2–3}

The SOLID ideas are

• The Single-responsibility principle: "There should never be more than one reason for a class to change."^[5] In other words, every class should have only one responsibility.^[6]
• The Open–closed principle: "Software entities ... should be open for extension, but closed for modification."^[7]
• The Liskov substitution principle: "Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it."^[8] See also design by contract.^[8]
• The Interface segregation principle: "Clients should not be forced to depend upon interfaces that they do not use."^[9][4]
• The Dependency inversion principle: "Depend upon abstractions, [not] concretes."^[10][4]

The SOLID acronym was introduced later, around 2004, by Michael Feathers.^[11]

Although the SOLID principles apply to any object-oriented design, they can also form a core philosophy for methodologies such as agile development or adaptive software development.^[3]

See also

• Code reuse
• GRASP (object-oriented design)
• Inheritance (object-oriented programming)
• List of software development philosophies

References

1. Martin, Robert C. "Principles Of OOD". ButUncleBob.com. from the original on Sep 10, 2014. Retrieved 2014-07-17.. (Note the reference to "the first five principles", although the acronym is not used in this article.) Dates back to at least 2003.
2. Martin, Robert C. (13 Feb 2009). "Getting a SOLID start". Uncle Bob Consulting LLC (Google Sites). from the original on Sep 17, 2013. Retrieved 2013-08-19.
3. Metz, Sandi (May 2009). "SOLID Object-Oriented Design". YouTube. Archived from the original on 2021-12-21. Retrieved 2019-08-13. Talk given at the 2009 Gotham Ruby Conference.
4. Martin, Robert C. (2000). (PDF). objectmentor.com. Archived from the original on 2015-09-06.{{cite web}}: CS1 maint: unfit URL (link)
5. (PDF). objectmentor.com. Archived from the original on 2 February 2015.{{cite web}}: CS1 maint: unfit URL (link)
6. Martin, Robert C. (2003). Agile Software Development, Principles, Patterns, and Practices. Prentice Hall. p. 95. ISBN 978-0135974445.
7. (PDF). objectmentor.com. Archived from the original on 5 September 2015.{{cite web}}: CS1 maint: unfit URL (link)
8. (PDF). objectmentor.com. Archived from the original on 5 September 2015.{{cite web}}: CS1 maint: unfit URL (link)
9. (PDF). objectmentor.com. 1996. Archived from the original on 5 September 2015.{{cite web}}: CS1 maint: unfit URL (link)
10. (PDF). objectmentor.com. Archived from the original on 5 September 2015.{{cite web}}: CS1 maint: unfit URL (link)
11. Martin, Robert (2018). Clean Architecture: A Craftsman's Guide to Software Structure and Design. p. 58. ISBN 9780134494166.