#caseOf:otherwise:
http://ja.doukaku.org/comment/5174/
Smalltalk版switch。直感的で解りやすい。
!Object methodsFor: 'switching'! caseOf: cases cases do: [:a| self = a key value and: [ ^a value value ] ]. ^nil! caseOf: cases otherwise: owBlock ^(self caseOf: cases) ifNil: owBlock!