Inheritance in Ruby

Explaination of Ruby inheritance and method dispatch. For Ruby Talks at PGS Software

Transcript

1. RUBY INHERITANCE MAINLY METHOD DISPATCH Created by Maciej Rząsa
2. WHERE IS MY S U P E R ?
3. CLASSES c l a s s A d e f f o o p r i n t " A " e n d e n d c l a s s B < A d e f f o o s u p e r p r i n t " B " e n d e n d p u t s B . n e w . f o o # > > " A B "
4. MODULES m o d u l e I n c l u d e d e f f o o ; s u p e r ; p r i n t " I " ; e n d e n d m o d u l e P r e p e n d d e f f o o ; s u p e r ; p r i n t " P " ; e n d e n d c l a s s A d e f f o o ; p r i n t " A " ; e n d e n d c l a s s B < A i n c l u d e I n c l u d e p r e p e n d P r e p e n d d e f f o o ; s u p e r ; p r i n t " B " ; e n d e n d p u t s B . n e w . f o o # > > " A I B P "
5. INCLUDE USAGE multiple inheritance (interface and implementation) use glue methods as interface (e.g. # e a c h for E n u m e r a b l e ) wrap inherited methods (aspect-oriented programming)
6. WRAP INHERITED METHODS m o d u l e S a v e W r a p p e r d e f s a v e p u t s " s a v e c a l l i n g " s u p e r e n d e n d c l a s s A < A c t i v e R e c o r d : : B a s e i n c l u d e S a v e W r a p p e r e n d A . n e w . s a v e Strange? Rails is built this way ;-)
7. PREPEND USAGE override methods not owned by the team (e.g. gems) alternative to reopening classes
8. BONUS: DEFINING METHOD FOR ONE OBJECT m o d u l e I n c l u d e d e f f o o ; s u p e r ; p r i n t " I " ; e n d e n d m o d u l e P r e p e n d d e f f o o ; s u p e r ; p r i n t " P " ; e n d e n d c l a s s A d e f f o o ; s u p e r ; p r i n t " A " ; e n d e n d c l a s s B < A i n c l u d e I n c l u d e p r e p e n d P r e p e n d d e f f o o ; s u p e r ; p r i n t " B " ; e n d e n d b = B . n e w d e f b . f o o ; s u p e r ; p r i n t " N N N " e n d b . f o o # > > A I B P N N N
9. DEFINING METHOD FOR ONE OBJECT: USAGE c l a s s A d e f s e l f . f o o p r i n t " A " e n d e n d
10. PRIVATE VS PROTECTED
11. PRIVATE c l a s s F o o p r i v a t e d e f b a r ; ' b a r ' e n d e n d c l a s s B a z < F o o d e f c h e c k _ b a r p u t s b a r p u t s s e l f . b a r r e s c u e p u t s ' s e l f p a r e n t N o M e t h o d E r r o r ' p u t s s e l f . q u x r e s c u e p u t s ' s e l f s e l f N o M e t h o d E r r o r ' p u t s P a r e n t . n e w . b a r r e s c u e p u t s ' n e w N o M e t h o d E r r o r ' p u t s P a r e n t . n e w . s e n d ( : b a r ) r e s c u e p u t s ' n e w N o M e t h o d E r r o r ' e n d p r i v a t e d e f q u x p u t s " q u x " e n d e n d B a z . n e w . c h e c k _ b a r # b a r # s e l f p a r e n t N o M e t h o d E r r o r # s e l f s e l f N o M e t h o d E r r o r # n e w N o M e t h o d E r r o r # b a r
12. PROTECTED c l a s s F o o p r o t e c t e d d e f b a r ; ' b a r ' e n d e n d c l a s s B a z < F o o d e f c h e c k _ b a r p u t s b a r p u t s s e l f . b a r r e s c u e p u t s ' s e l f p a r e n t N o M e t h o d E r r o r ' p u t s s e l f . q u x r e s c u e p u t s ' s e l f s e l f N o M e t h o d E r r o r ' p u t s P a r e n t . n e w . b a r r e s c u e p u t s ' n e w N o M e t h o d E r r o r ' e n d p r o t e c t e d d e f q u x " q u x " e n d e n d B a z . n e w . c h e c k _ b a r # b a r # b a r # q u x # n e w N o M e t h o d E r r o r
13. USAGE Protected comparison mutator methods for immutable objects internal API for an object (e.g. A c t i o n C o n t r o l l e r : : C a c h i n g ) Private Not tested methods Internals Other use # p u b l i c _ s e n d if in doubt ;-)