为什么这样做有效，我在最大索引后切片了1个，却没有出现错误? [英] Why does this work, I am slicing 1 past max index and not getting an error?

问题描述

我正在玩切片，但发现了一些我无法解释的内容.我创建了一个总长度为10的字符串(索引范围从0到9)，然后从中创建一个切片，该切片指定了一个超出最大索引的值，并且它不会出现混乱.如果我超过上一个指数不止一个，那将会恐慌.请问我不明白什么?

I was playing around with slices, and I found something that I can't explain. I create a string of total length 10 (index ranges from 0 to 9) and then I create a slice from it specifying one past the max index and it does not panic. It will panic if I go more than one past the last index. What am I not understanding please?

我研究了整数切片，并认为字符串可能有些奇怪，但表现出相同的行为.

I have investigated with integer slices as well thinking there might be something odd about strings, but it showed the same behavior.

这里是一个示例:我预期在 x:= str [10:] 处失败.

Here is an example: I expected a failure at x:= str[10:].

package main

import "fmt"

func main() {

    var str = "attribute="

    x := str[10:]
    fmt.Printf("type of x is %T\n", x)
    //fmt.Printf("x is a %T and length of x is %d\n", x, len(x))

    for k, v := range []byte(str) {
        fmt.Printf("%d, %x\n", k, v)
    }

}

游乐场: https://play.golang.org/p/Z-3YvTx3-s6

输出:

type of x is string
0, 61
1, 74
2, 74
3, 72
4, 69
5, 62
6, 75
7, 74
8, 65
9, 3d

推荐答案

它位于规范.允许 low 或 high 等于长度.

It's in the spec. Having low or high equal to the length is allowed.

对于数组或字符串，如果 0< =低< =高< = len(a)，则索引在范围内，否则它们不在范围内.

For arrays or strings, the indices are in range if 0 <= low <= high <= len(a), otherwise they are out of range.

关于这为什么不是错误":您可以将切片操作可视化为在元素之间切割 .像这样:

As to "why is this not an error": you can visualize the slicing operation as cutting between the elements. Like this:

│   a   t   t   r   i   b   u   t   e   =    │
│ ↑   ↑   ↑   ↑   ↑   ↑   ↑   ↑   ↑   ↑   ↑  │
│ 0   1   2   3   4   5   6   7   8   9   10 │

从技术上讲，切片点10仍在范围内，但之后没有任何元素.这就是为什么 [10:] 生成空字符串的原因(或者是因为 low 和 high 之间没有元素).例如，这在红宝石中的工作方式相同.也许还有其他语言.

Technically slice point 10 is still within bounds, but it has no elements after it. That's why [10:] results in an empty string (that, or because there are no elements between low and high). This works the same way in ruby, for example. Maybe other languages too.

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