GO 切片问题求教

[jzl]

初始化切片 s := make([]int, 3) 取 s[3:] 不会报越界错误，取 s[4:]就会越界了， 求教啊

[Leigg]

这个还真没碰见过，是冷知识？

[c0011]

s[3:] 是扩展切片，3 代表的是个数不是下标。

[c0011]

我上边的不对。可能就是语言的规定吧，3 代表最后一个元素并且是空(nil?)

[kidlj]

> For arrays or strings, the indices are in range if 0 <= low <= high <= len(a), otherwise they are out of range. For slices, the upper index bound is the slice capacity cap(a) rather than the length.

ref: https://golang.org/ref/spec#Slice_expressions

原因未知 :)

[c0011]

@kidlj 但是 fmt.Println(s[3]) 会报错

[kidlj]

> The indices low and high select which elements of operand a appear in the result. The result has indices starting at 0 and length equal to high - low

> For convenience, any of the indices may be omitted. A missing low index defaults to zero; a missing high index defaults to the length of the sliced operand.

因此 s[3:] == s[3:len(a)] = s[3:3] ✓
s[4:] == s[4:len(a)] == s[4:3] x

[kidlj]

@c0011

> the index x is in range if 0 <= x < len(a), otherwise it is out of range

ref: https://golang.org/ref/spec#Index_expressions

[kidlj]

修正：len(s) 不是 len(a)

[gamexg]

故意的吧，
如果 s[3:]就报错，就无法取末尾的空切片了。

[Vegetable]

错误信息是
panic: runtime error: slice bounds out of range [4:3]
6 楼说的应该就是正确答案了.

[shijiu]

缺少的最高位是切片长度，而最高位是开区间，取 s[3:3]的话返回一个 0 长切片，应该是一个规定吧，方便判断。
就和 s[:0]返回一个 0 长切片一样？

[dreampuf]

https://github.com/golang/go/blob/master/src/runtime/error.go#L110

[Carseason]

s[3:3]
s[4:3]