Ruby中二维数组插入元素的问题

Question

我想在某一个数组中插入元素，代码如下：

foo = Array.new(10,[])
foo[0] << 1
puts foo.to_s

输出的结果是

[[1], [1], [1], [1], [1], [1], [1], [1], [1], [1]]

这是为什么啊？

如果是哈希的话

bar = Hash.new([])
bar[0] << 1
puts bar.to_s
puts bar[1].to_s

输出的结果是

{}
[1]

更加摸不着头脑了……求指教……

Answer 1

foo = Array.new(10,[])

The 10 empty arrays created by this method are the same Object

If you want to create different Objects, please use the following method.

foo = Array.new(10) { Array.new }

Reference: http://ruby-doc.org/core-2.0.0/Array.html#label-Creating+Arrays

Answer 2

To add to the above, all object_ids are the same
foo.map(&:object_id)
=> [9298880, 9298880, 9298880, 9298880, 9298880, 9298880, 9298880, 9298880, 9298880, 9298880]

Answer 3

I usually use map.
(1..10).map {[]}

But I still have a question, why is it still the same Array?