Ruby Metaprogramming
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Ruby metaprogramming involves writing code that manipulates language constructs at runtime. Some key aspects of Ruby metaprogramming discussed in the document include: 1. Objects, classes, and modules - Classes are objects and classes look up methods via objects and modules in their ancestors chain. Modules can be included to add methods. 2. Singleton methods and metaclasses - Each object has a hidden metaclass that holds its singleton methods. Class methods are defined on the metaclass. 3. Dynamic method definition - Methods can be defined dynamically at runtime via open classes, modules, and metaclasses. Various eval methods also allow evaluating code to modify classes, modules, and objects.
Ruby Metaprogramming
- 2. About me Lu Wei Jen http://blog.weijen.net http://www.facebook.com/weijenlu Twitter: weijenlu
- 3. Metaprogramming Metaprogramming is writing code that manipulates language constructs at runtime.
- 4. Agenda Object, Class and Module Singleton Methods and Metaclass Block Eval family
- 5. Part 1. Object, Class and Module Object introspection Classes Module Singleton Method Method Lookup Dynamic Methods Hook methods
- 7. Metaprogramming Ruby p.38 Objects of the same class share methods, but they don’t share instance variables.
- 8. Classes Classes themselves are nothing but objects . Classes are instances of a class called Class .
- 9. Method Lookup One step to the right, then up. obj @val MyClass my_method() class() Object
- 10. Open Class You can always reopen existing classes, and modify them.
- 11. Module Modules are also objects. When you include a module: Ruby creates an anonymous class wraps the module. Ruby then insert anonymous class into the ancestors chain.
- 12. Module obj @val Myclass my_method (M) m_method Object class
- 13. Singleton Method
- 14. Class Method are Singleton Method
- 15. Metaclass Where is singleton method? An object can have its own special, hidden class named Metaclass. Also named eigenclass. obj @val Myclass my_method (M) m_method Object class
- 16. Metaclass
- 19. Method Lookup Review obj @val MyClass my_method (M) m_method Object class #obj my_singleton_method #MyClass class_method_1 class_method_2 #(M) m_class_method #Object
- 22. method_missing() If method can’t be find, then self calling method_missing(). It’s an instance method of Kernel that every object inherits. It responded by raising a NoMethodError .
- 25. Hook methods inherited() included()
- 26. Part 2. Block Block Scope Callable Objects
- 27. Block
- 28. Scope (But don’t do that)
- 29. Scope Gates Class definitions Module definitions methods
- 30. Proc Object
- 31. The & Operator A block can be an argument to a method. Block argument: must be the last in the list of arguments. Must prefixed by an & sign. & operator convert the block to a Proc object. & operator also can convert the Proc object to block.
- 32. The & Operator
- 33. Part 3. Eval* family eval instance_eval module_eval(class_eval)
- 34. Kernel#eval() it takes a string of code. It executes the code in the string.
- 35. The troble with eval() Your editor’s features mayn’t support. Not easy to read and modify. Not easy to debug. Code Injection
- 38. Classes themselves are nothing but objects .
- 39. Thanks
- 40. Q&A