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Lessons in Software Evolution Learned by Listening to Smalltalk

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Invited talk at SOFSEM 2010.
Full paper (PDF) is available for download.
http://bit.ly/8awi30

Published in: Technology, Education
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Lessons in Software Evolution Learned by Listening to Smalltalk

  1. 1. Lessons in Software Evolution Learned by Listening to Smalltalk Oscar Nierstrasz scg.unibe.ch
  2. 2. Research Team Adrian Lienhard Adrian Kuhn Fabrizio Perin Lukas Renggli Jorge Ressia David Roethlisberger Niko Schwarz Toon Verwaest Erwann Wernli
  3. 3. Roadmap The trouble with change Smalltalk in a Nutshell Taming Software Change Epilogue — Bringing Models Closer to Code
  4. 4. Roadmap The trouble with change Smalltalk in a Nutshell Taming Software Change Epilogue — Bringing Models Closer to Code The trouble with change
  5. 5. How we enable change Package what is stable Define an interface for configuration
  6. 6. A brief history of software packaging
  7. 7. The Trouble with Software Change Understanding the system Bridging the gap Specifying change Managing change Understanding change
  8. 8. Roadmap The trouble with change Smalltalk in a Nutshell Taming Software Change Epilogue — Bringing Models Closer to Code Smalltalk in a Nutshell
  9. 9. To thine own self be true Less is More The object model “is as simple as possible, but no simpler” Reify Everything You can change a Running System “ Everything is an object” is applied consistently Smalltalk models itself, so changing the model changes the system
  10. 10. The origins of Smalltalk Alan Kay’s Dynabook project (1968) Alto — Xerox PARC (1973)
  11. 11. Smalltalk architecture Image Changes Virtual machine Sources
  12. 12. Everything happens by sending messages 2 raisedTo: 1 + 3 factorial 128 First unary, then binary, then keyword: factorial + raisedTo:
  13. 13. A typical method <= aPoint &quot;Answer whether the receiver is neither below nor to the right of aPoint.&quot; ^ x <= aPoint x and: [y <= aPoint y] (2@3) <= (5@6) true Keyword message Instance variable Block Binary message Unary message Method name Argument Comment Return
  14. 14. Everything is an object
  15. 15. Everything is an object
  16. 16. You can change a running system AKA: “The Debugger is your Friend”
  17. 17. Pharo — an multi-platform, open-source Smalltalk Pharo by Example . Andrew Black, et al. Square Bracket Associates, 2009.
  18. 18. Roadmap The trouble with change Smalltalk in a Nutshell Taming Software Change Epilogue — Bringing Models Closer to Code Taming Software Change
  19. 19. Moose: a platform for reverse engineering
  20. 20. Explicit metamodels enable change Smalltalk Extensible meta model Model repository The Story of Moose: an Agile Reengineering Environment. Oscar Nierstrasz, Stéphane Ducasse, and Tudor Gîrba. ESEC/FSE 2005 Navigation Metrics Querying Grouping Smalltalk Java C++ COBOL … CDIF XMI External Parser CodeCrawler ConAn Van ... Hapax
  21. 21. Moose visualizations
  22. 22. Programming visualizations with CodeCrawler
  23. 23. Scripting visualizations with Mondrian Mondrian: An Agile Visualization Framework. Michael Meyer, Tudor Gîrba, and Mircea Lungu. SoftVis 2006
  24. 24. Moose — a platform for collaborative research
  25. 25. Feature inheritance ≠ specialization
  26. 26. First-class traits enable fine-grained reuse
  27. 27. Class = superclass + state + traits + glue Traits provide and require methods The composing class retains control Traits: A Mechanism for fine-grained Reuse. Stéphane Ducasse, Oscar Nierstrasz, Nathanael Schärli, Roel Wuyts and Andrew Black. ACM TOPLAS, March 2006
  28. 28. Traits and Classes share common behaviour
  29. 29. First-class aliases enable object flow analysis Practical Object-Oriented Back-in-Time Debugging. Adrian Lienhard, Tudor Gîrba, and Oscar Nierstrasz. ECOOP 2008.
  30. 30. A back-in-time VM with object flow analysis
  31. 31. GC remembers only what is needed
  32. 32. How to manage change in a running system? Encapsulating and Exploiting Change with Changeboxes. Marcus Denker, et al. ICDL 2007.
  33. 33. First-class changes enable scoped evolution
  34. 34. Roadmap The trouble with change Smalltalk in a Nutshell Taming Software Change Epilogue — Bringing Models Closer to Code Epilogue — Bringing Models Closer to Code
  35. 35. Systems that support change need to be model-centric and context-aware Model-centric systems are self-describing and can be adapted dynamically Context-aware systems control the scope of change to static or dynamic contexts

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