Visitors Framework Generator
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This document discusses the visitor pattern and presents the Visitors Framework Generator (VFG). The VFG automatically generates model-specific visitor frameworks from Ecore metamodels. It creates visitor and visitable interfaces as well as default abstract visitor implementations. This avoids duplicating code and separates structure from behavior. The VFG was used to generate visitors for the Eclipse OCL and QVTd modeling projects, creating frameworks for 7 and 10 Ecore metamodels respectively. The visitor pattern and VFG are useful when behavior is unclear or evolving, and allows clients to add specific behavior algorithms without changing structure.
Visitors Framework Generator
- 1. Visitors Framework Generator Computer Science Department University of York Adolfo S¨¢nchez-Barbudo Herrera (asbh500@york.ac.uk)
- 2. Agenda ¡ñ Visitor Pattern ¡ñ Visitors Framework Generator ¡ð Overview ¡ð Model traversals ¡ð Visitors framework ¡ð Example ¡ñ Visitors in Eclipse OCL/QVTd ¡ñ Conclusions 2
- 3. Visitor Pattern ¡ñ OOP design pattern ¡ñ Separate structure from behaviour 2
- 4. Visitor Pattern II ¡ñ Add/Remove/Modify/Replace behaviour without changing structure. ¡ð Ideal when working with third party structures. 3
- 5. Visitor Pattern III ¡ñ Main disadvantage ¡ð It¡¯s not the ideal pattern with evolving structures. 4
- 6. Visitor Pattern IV ¡ñ Visitors applied to modeling languages 5
- 7. Visitors Framework Generator ¡ñ VFG Overview VFG Ecore Model Visitable Model Implementation Visitor/ Visitable Interfaces Abstract Visitors Impl. Model-Specific Visitors Framework Manual Visitors Generated Visitors More MDE-based generators Manual Generated 6
- 8. Visitor Generation Framework II ¡ñ Visitable implementation from Ecore MM 7
- 9. Visitor Generation Framework III ¡ñ Ecore MM specific visitors framework 1. Visitor/Visitable Interfaces 2. Default Abstract Implementations ¡ñ Contextful Visitor ¡ñ Null Visitor ¡ñ Extending Visitor ¡ñ Delegating Visitor ¡ñ ... 8
- 11. Model Traverals II ¡ñ Traversal in accept method ¡ð Doomed to the same traversal algorithm. 10 ¡ñ Traversal in client code ¡ð Ok, but traversal is part of the algorithm ¡ñ Traversal in visitors ¡ð Best, but more patterns for reuse sake Traversal Visitor Action
- 15. Example 14
- 16. Visitors Usage in Eclipse OCL/QVTd ¡ñ Eclipse OCL ¡ð 7 Ecore metamodels ¡ð 48 generated abstract visitors ¡ð 67 manual visitors ¡ñ Eclipse QVTd ¡ð 10 Ecore metamodels ¡ð 89 generated abstract visitors ¡ð 76 manual visitors 15
- 17. Conclusions ¡ñ VFG: ¡ð Automatically brings the benefits of the visitor pattern to Ecore-based models ¡ð Automatically creates a MM-specific framework to leverage visitors creation ¡ð It?s a convenient practice when your models have unclear behaviour or an evolving one ¡ð It?s a key practice to let clients add their specific behaviour algorithms ¡ð A key tool in the development of Eclipse OCL/QVTd 16
- 18. Thank you very much Questions ? doubts, feedback, enquiries, etc. to asbh500@york.ac.uk