Metaprogramming in Ruby

A presentation on metaprogramming in ruby

Transcript

1. Metaprogramming in Ruby Created By Kristen Mills
2. What is Metaprogramming?
3. The Basics
4. Symbols Kind of like strings Immutable Not garbage collected
5. Blocks That do...end thing or curly braces if on one line One of the 3 types of closures
6. Monkey Patching
7. Monkey Patching by example c l a s s S t r i n g d e f m y _ m e t h o d " m y _ m e t h o d i s a c o o l m e t h o d " e n d e n d ' a b c ' . m y _ m e t h o d # = > " m y _ m e t h o d i s a c o o l m e t h o d "
8. Refinements Allows you to monkey patch in a given scope
9. Aliasing method alias method_1, method_2 alias_method :method_1, :method_2
10. Defining Methods def method_name(params) define_method(name, &block) define_singleton_method(name, &block)
11. Instance Variables instance_variable_set(name, value) instance_variable_get(name)
12. attr_accessor d e f a t t r _ a c c e s s o r ( * a r g s ) a r g s . e a c h d o | a r g | d e f i n e _ m e t h o d ( a r g ) d o i n s t a n c e _ v a r i a b l e _ g e t ( : " @ # { a r g } " ) e n d d e f i n e _ m e t h o d ( : " # { a r g } = " ) d o | v a l u e | i n s t a n c e _ v a r i a b l e _ s e t ( : " @ # { a r g } " , v a l u e ) e n d e n d e n d
13. Eigenclasses!
14. Wait, where does that method go?
15. Accessing the Eigenclass e i g e n c l a s s = c l a s s < < o b j c l a s s < < a n _ o b j e c t # y o u r c o d e h e r e e n d
16. Before you ask Yes, eigenclasses have Eigenclasses
17. Calling Methods send(name, *args)
18. Removing Methods remove_method(name) undef_method(name)
19. Rails Black Magic (aka Method Missing)
20. Method Missing method_missing(method, *args, &block)
21. Domain Specific Languages
22. Evaluating Strings/Blocks eval(string) instance_eval(string) instance_eval(&block) instance_exec(*args, &block) yield(*args) call(*args)
23. Vending Machine f i n i t e i n i t i a l : : i d l e d o b e f o r e : i d l e d o @ c u r r e n t _ m o n e y = 0 e n d a f t e r : a c c e p t i n g d o p u t s " C u r r e n t a m o u n t i n m a c h i n e : $ % . 2 f " % @ c u r r e n t _ m o n e y e n d @ m o n e y . e a c h d o | e v e n t _ n a m e , a m o u n t | e v e n t : " i n s e r t _ # { e v e n t _ n a m e } " d o b e f o r e d o p u t s " A d d i n g # { e v e n t _ n a m e } " a d d _ m o n e y ( a m o u n t ) e n d g o f r o m : : i d l e , t o : : a c c e p t i n g g o f r o m : : a c c e p t i n g , t o : : a c c e p t i n g e n d e n d @ p r o d u c t s . e a c h d o | e v e n t _ n a m e , p r i c e | e v e n t : " b u y _ # { e v e n t _ n a m e } " d o b e f o r e { p u t s " B u y i n g # { e v e n t _ n a m e } " } g o f r o m : : a c c e p t i n g , t o : : v e n d i n g , i f : l a m b d a { @ c u r r e n t _ m o n e y > = p r i c e } a f t e r d o @ c u r r e n t _ m o n e y - = p r i c e e n d e n d e n d e v e n t : c o m p l e t e _ v e n d d o b e f o r e { p u t s " R e t u r n i n g $ % . 2 f t o t h e c u s t o m e r " % @ c u r r e n t _ m o n e y } g o f r o m : : v e n d i n g , t o : : i d l e e n d e v e n t : p r e s s _ c o i n _ r e t u r n d o
24. add_event d e f a d d _ e v e n t ( e v e n t _ n a m e , & b l o c k ) # S o m e o t h e r s t u f f h a p p e n s b e f o r e h e r e @ c l a s s . s e n d ( : d e f i n e _ m e t h o d , : " c a n _ # { e v e n t _ n a m e } ? " ) d o e v e n t . t r a n s i t i o n s . k e y ? c u r r e n t _ s t a t e . n a m e e n d @ c l a s s . s e n d ( : d e f i n e _ m e t h o d , : " # { e v e n t _ n a m e } " ) d o i f e v e n t . t r a n s i t i o n s . k e y ? c u r r e n t _ s t a t e . n a m e t r a n s i t i o n = e v e n t . t r a n s i t i o n s [ c u r r e n t _ s t a t e . n a m e ] u n l e s s t r a n s i t i o n . c o n d i t i o n . n i l ? o r s e l f . i n s t a n c e _ e x e c ( & t r a n s i t i o n . c o n d i t i o n ) r a i s e E r r o r . n e w ( ' D o e s n o t m e e t t h e t r a n s i t i o n c o n d i t i o n ' ) e n d n e w _ s t a t e = s t a t e s [ e v e n t . t r a n s i t i o n s [ c u r r e n t _ s t a t e . n a m e ] . t o ] e v e n t . c a l l b a c k s [ : b e f o r e ] . e a c h d o | c a l l b a c k | s e l f . i n s t a n c e _ e v a l & c a l l b a c k e n d # M o r e c a l l b a c k s h a p p e n h e r e @ c u r r e n t _ s t a t e = n e w _ s t a t e # M o r e C a l l b a c k s h a p p e h e r e e v e n t . c a l l b a c k s [ : a f t e r ] . e a c h d o | c a l l b a c k | s e l f . i n s t a n c e _ e v a l & c a l l b a c k e n d s e l f e l s e r a i s e E r r o r . n e w ' I n v a l i d T r a n s i t i o n ' e n d e n d e n d
25. Any Questions?
26. Thanks!