为什么go不报告“切片范围超出范围"?在这种情况下? [英] Why go doesn't report "slice bounds out of range" in this case?

问题描述

以下是要复制的代码:

package main

import "fmt"

func main() {
    var v []int
    v = append(v,1)
    v = append(v,v[1:]...)
    fmt.Println("hi", v)

}

v[1]将报告index out of range，但v[1:]...不会，为什么?

v[1] will report index out of range, but v[1:]... won't, why?

推荐答案

这就是spec定义切片表达式的方式

That's how spec defines slice expressions

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.对于切片，索引的上限是切片容量cap(a)而不是长度.

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.

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

这就是切片的索引表达式的定义方式

And that's how index expressions for slices are defined

如果0< = x<则索引x在范围内. len(a)，否则超出范围

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

如果x在运行时超出范围，则会发生运行时恐慌

if x is out of range at run time, a run-time panic occurs

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

以您的示例为例:

v[1]恐慌，因为它属于上述定义的范围(因为1不符合0 <= x < len(a)的要求)

v[1] panics because it's our of range as per the definition above (because 1 does not qualify the 0 <= x < len(a) reqirement)

v[1:]运行正常，因为它与v[1:len(v)]相同并且符合if 0 <= low <= high <= cap(a)的要求.

v[1:] runs fine because it's identical to v[1:len(v)] and fits the if 0 <= low <= high <= cap(a) requirement.

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