case 调用的是 === 方法

obj === other → true or false

Case Equality – For class Object, effectively the same as calling #==, but typically overridden by descendants to provide meaningful semantics in case statements.

http://codemacro.com/2012/07/26/ruby-case-when/

比如你是叫李狗蛋的人类,  说你是李狗蛋成立, 说你是人类也成立嘛  

如果条件是一个类名的话，可以判断分歧变量是不是属于该类，这里就是用于类型判定了。