Visitors Framework Generator

Computer Science DepartmentUniversity of York

Adolfo Sánchez-Barbudo Herrera (asbh500@york.ac.uk)

Agenda

● Visitor Pattern● Visitors Framework Generator

○ Overview○ Model traversals○ Visitors framework○ Example

● Visitors in Eclipse OCL/QVTd● Conclusions

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Visitor Pattern● OOP design pattern● Separate structure from behaviour

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Visitor Pattern II

● Add/Remove/Modify/Replace behaviour without changing structure.○ Ideal when working with third party structures.

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Visitor Pattern III

● Main disadvantage○ It’s not the ideal pattern with evolving structures.

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Visitor Pattern IV

● Visitors applied to modeling languages

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Visitors Framework Generator

● VFG Overview

VFGEcoreModel

VisitableModel

Implementation

Visitor/Visitable

Interfaces

AbstractVisitors

Impl.

Model-Specific Visitors Framework

ManualVisitors

GeneratedVisitors

More MDE-basedgenerators

Manual Generated

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Visitor Generation Framework II

● Visitable implementation from Ecore MM

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Visitor Generation Framework III

● Ecore MM specific visitors framework

1. Visitor/Visitable Interfaces

2. Default Abstract Implementations

● Contextful Visitor● Null Visitor● Extending Visitor● Delegating Visitor● ...

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Model traversals9

Model Traverals II

● Traversal in accept method○ Doomed to the same traversal algorithm.

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● Traversal in client code○ Ok, but traversal is part of the algorithm

● Traversal in visitors○ Best, but more patterns for reuse sake

Traversal

Visitor

Action

Visitors Framework 11

Visitors Framework II12

Visitors Framework III13

Example14

Visitors Usage in Eclipse OCL/QVTd

● Eclipse OCL○ 7 Ecore metamodels○ 48 generated abstract visitors○ 67 manual visitors

● Eclipse QVTd○ 10 Ecore metamodels○ 89 generated abstract visitors○ 76 manual visitors

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Conclusions

● VFG:○ Automatically brings the benefits of the visitor

pattern to Ecore-based models○ Automatically creates a MM-specific framework to

leverage visitors creation○ It´s a convenient practice when your models have

unclear behaviour or an evolving one○ It´s a key practice to let clients add their specific

behaviour algorithms○ A key tool in the development of Eclipse OCL/QVTd

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Thank you very much

Questions ?

doubts, feedback, enquiries, etc. to asbh500@york.ac.uk