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Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
Ruby Metaprogramming 08
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Ruby Metaprogramming 08

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An introductory presentation about Ruby metaprogramming presented at CodeMash '08

An introductory presentation about Ruby metaprogramming presented at CodeMash '08

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Transcript

  • 1. Rails A Peek under the covers Brian Sam-Bodden
  • 2. Rails
  • 3. A framework... for building database-backed web applications that at first wow us with speed
  • 4. Rails can be seen as a collection of... mini-languages for implementing MVC on the web
  • 5. then came the headlines... and we all wondered... what am I doing wrong?
  • 6. the answer too much and we reacted the way we knew better ...with frameworks
  • 7. Lessons of Rails
  • 8. Integrated Seamless front to back stack Familiar idioms on every tier Avoiding manually defining or gluing the tiers
  • 9. CoC Convention Over Configuration “Flexibility is overrated, Constraints are liberating”
  • 10. DRY Do it once, do it right and do it in the right place
  • 11. Instant Change Tight feedback loop We want the world and we want it NOW!
  • 12. Terse Expressiveness Getting advanced behavior with very little code Without sacrificing readability
  • 13. Did the clones catch up? Yes , Sort of and Not quite ✓CoC ✓DRY ๏ Terse Expressiveness ✓ Instant Change ✓Integrated
  • 14. What’s Missing?
  • 15. ✓Object-Oriented ✓Elegant ✓General Purpose ✓ Multi-paradigm Ruby ✓ Interpreted is... ✓Reflective ✓Dynamic ✓ Garbage-collected
  • 16. Without Ruby there would be no Rails Ruby’s Dynamism is the key ingredient to the Rails framework
  • 17. Open Classes
  • 18. Say we have an Array like: [1,2,3,4,5] and we want to sum of all of its elements
  • 19. Let’s try something like: [1,2,3,4,5].sum Doh! Doesn’t work in Ruby … yet!
  • 20. Ruby classes are open We can teach the Array class a new behavior
  • 21. Let’s try again! Load the file containing the enhancements
  • 22. Since Ruby classes are open... You can statically enhance ANY class
  • 23. Code as Data
  • 24. When code can be manipulated as data a whole world of possibilities opens In Ruby you can evaluate the contents of a string
  • 25. Code that spits out code
  • 26. Ruby provides the eval family of methods for runtime execution of code stored in strings eval will evaluate any string
  • 27. instance_eval can evaluate a string or a code block in the context of the receiver
  • 28. class_eval can evaluate a string or a code block in the context of the class or module it is called on
  • 29. Meta-programming
  • 30. Meta-programming ...is about programs that write programs ...it’s a superb tool for building frameworks ...it’s the key ingredient for building domain-specific languages
  • 31. Ruby is a great language for meta-programming because ...is dynamic and reflexive ...open and malleable ...code is data, data is code ...clean unencumbered syntax ...programming event model
  • 32. Rails ...uses the Ruby meta-programming techniques to accomplish most of its “magic” ...uses meta-programming to bring the language closer to the problem at hand ...is a domain-specific language for building web applications
  • 33. Singleton Class
  • 34. All objects are open to modification You can change a particular instance of a class Ruby uses a proxy class known as the singleton class Meta-class: The singleton for Class objects
  • 35. With access to a class object’s meta-class we can then use Ruby meta-programming techniques to enhance the class
  • 36. Rails relies heavily on Ruby’s ability to dynamically enhance a class
  • 37. The previous example could have also been accomplished using the define_method
  • 38. Accessing the singleton meta-class explicitly
  • 39. Inheritance the Ruby Way
  • 40. Ruby Meta-programming techniques can be used to write DSLs that use class methods to enhance subclasses Using the meta-class (singleton class) of the subclasses Rails uses this technique in ActiveRecord
  • 41. Let’s create a module with a “Base” class
  • 42. Methods get added to our classes with simple declarations Can you say DSL!
  • 43. Rails uses this technique in ActiveRecord Now our class has a new set of class methods
  • 44. AOP the Ruby Way
  • 45. With alias_method you can wrap an existing method
  • 46. Meta-Programming Events
  • 47. Included Hook
  • 48. Ruby has a rich event model associated with static and dynamic changes of the code
  • 49. Method Missing
  • 50. Ruby provides several hook methods that can be used to created custom behaviors method_missing method_added method_removed
  • 51. Let’s implement the greeter example using method_missing
  • 52. There is more to Ruby than Rails! Building a Framework? Give Ruby a try! Build the language up towards the problem Meta-programming is no longer just for the Lisp folks The future? Powerful Java APIs exposed with Ruby DSLs
  • 53. www.integrallis.com

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