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Ruby Metaprogramming
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.
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Ruby Metaprogramming
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- 2. About me LuWei Jen http://blog.weijen.net http://www.facebook.com/weijenlu Twitter: weijenlu
- 3. Metaprogramming Metaprogramming iswriting code that manipulates language constructs at runtime.
- 4. Agenda Object, Classand 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
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- 7. Metaprogramming Ruby p.38Objects of the same class share methods, but they don’t share instance variables.
- 8. Classes Classes themselvesare nothing but objects . Classes are instances of a class called Class .
- 9. Method Lookup Onestep to the right, then up. obj @val MyClass my_method() class() Object
- 10. Open Class Youcan always reopen existing classes, and modify them.
- 11. Module Modules arealso 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 @valMyclass my_method (M) m_method Object class
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- 14. Class Method areSingleton Method
- 15. Metaclass Where issingleton 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
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- 19. Method Lookup Reviewobj @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
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- 22. method_missing() If methodcan’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 .
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- 25. Hook methods inherited()included()
- 26. Part 2. BlockBlock Scope Callable Objects
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- 28. Scope (But don’tdo that)
- 29. Scope Gates Classdefinitions Module definitions methods
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- 31. The & OperatorA 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.
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- 33. Part 3. Eval*family eval instance_eval module_eval(class_eval)
- 34. Kernel#eval() it takesa string of code. It executes the code in the string.
- 35. The troble witheval() Your editor’s features mayn’t support. Not easy to read and modify. Not easy to debug. Code Injection
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- 38. Classes themselves arenothing but objects .
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