ruby - 为什么我不能改变 self 的值(value)？

Question

为什么我可以这样改变“self”:

self.map! {|x| x*2}

或者这样:

self.replace(self.map {|x| x*2})

但不是这样:

self = self.map {|x| x*2}

为什么 Ruby 不允许我更改“self”变量指向的对象，但允许我更改对象的属性？

Answer 1

不是答案，只是一个线索。

a=[1,2]
=>[1,2]
a.object_id
=>2938

a.map!{|x| x*2}
=>[2,4]
a.object_id  # different data but still the same object
=>2938

a.replace(a.map {|x| x*2})
=>[4,8]
a.object_id  # different data but still the same object
=>2938

a = a.map{|x| x*2} # .map will create a new object assign to a 
=>[8,16]
a.object_id  #different object
=>2940   

你不能把自己变成另一个。