Ruby array slicing - weird behavior

最新推荐文章于 2024-01-06 14:21:17 发布

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#Ruby #Array slice

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本文探讨了Ruby中数组切片操作的特殊行为，特别是当索引超出数组范围时返回nil或空数组的区别。通过构造示例展示了数组内部结构如何影响这种行为，并解释了为何特定索引会返回不同结果。

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If you play around array slicing in irb, it will behavior like below:

irb(main):027:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):028:0> a[2,1]      
=> [3]
irb(main):029:0> a[4,1]      
=> nil
irb(main):030:0> a[3,1]
=> []

The weird behavior is that sometimes it return empty array, and sometimes it return nil instead, why that? According to the ruby docs an array split should return nil if the start index is out of range. So why is it that a[3,1] is not returning nil?

Below is the reasonable explaination from StackOverflow:

The end of the array is [], but the end of the array plus 1 is nil. Look at it this way: the Array [1,2,3] can be considered to be constructed from cons cells as such: (1, (2, (3, ())), or 1:2:3:[]. The 3rd index (4th item) is then clearly [].