1. Credits
   1. slides
      1. Rafael Luque @rafael_luque
      2. John Wilson tug@wilson.co.uk
   2. photos
      1. http://www.flickr.com/photos/alancleaver/
      2. http://www.flickr.com/photos/lrargerich/
      3. http://www.flickr.com/photos/21306332@N07/
2. about
   1. me
      1. Groovy/Grails (sometimes Java) hacker
      2. test addicted and clean code lover
   2. Osoco
      1. Small but outstanding software development shop
      2. Groovy and Grails hackers
      3. on EC2 cloud nine
      4. TDD mantra singers
      5. Quality preachers
3. http://osoco.github.com/groovy-metakoans/
4. What is metaprogramming?
   1. Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data.
5. Metaobject protocol (MOP)
   1. definition
      1. An interpreter of the semantics of a program that is open and extensible
      2. determines what a program means and what is its behavior
      3. extensible - metaprogrammer can alter program behavior by extending parts of the MOP
      4. exposes some or all internal structure of the interpreter to the programmer
      5. set of classes and methods that allow a program to inspect the state of the supporting system and alter its behaviour
   2. vs Java Reflection API
      1. allows to explore the structure of your code...
      2. but still restricted to the static structure you have created
   3. Building parts
      1. GroovyObject
         1. implemented by every object in Groovy
      2. MetaObjectProtocol
         1. MOP API
      3. MetaClass
         1. extends MetaObjectProtocol
         2. methods for interacting with Groovy runtime (not interesting for MOP hackers)
      4. MetaClassRegistry
         1. holds metaclasses
         2. GroovyObject has a direct reference to MC
         3. lookup for POJOs
      5. GroovyInterceptable
         1. marker interface
         2. all methods should be intercepted through the invokeMethod
      6. Method dispatching logic
         1. class implements GroovyInterceptable?
            1. call it's invokeMethod()
            2. method exists in MetaClass or class?
            3. call it
            4. has a property with method name?
            5. is of type Closure?
            6. call Closure call() method
            7. has methodMissing()
            8. call it's methodMissing()
            9. has invokeMethod()?
            10. call it's invokeMethod()
            11. throw MissingMethodException
      7. Categories and mixins
         1. category
            1. use(ACategoryClass) { ... }
            2. injects methods
            3. only for the current thread
            4. only for the duration of the closure
         2. mixin
            1. AST transformation
            2. compile-time through annotations and AST transformations
            3. @Category defines injected behaviour
            4. @Mixin injects behaviour from a @Category
            5. run-time
            6. explicit call
            7. aClass.mixin CategoryClass