go - slice 索引大于长度且小于容量会产生错误

Question

以下代码在运行时会出错。

package main

import fmt "fmt"

func main(){

    type b []int
    var k = make([]b, 5, 10)
    fmt.Printf("%d\n",k[8])
    fmt.Printf("%d", len(k))
}

错误如下。

panic: runtime error: index out of range

runtime.panic+0x9e /go/src/pkg/runtime/proc.c:1060
        runtime.panic(0x453b00, 0x300203f0)
runtime.panicstring+0x94 /go/src/pkg/runtime/runtime.c:116
        runtime.panicstring(0x4af6c6, 0xc)
runtime.panicindex+0x26 /go/src/pkg/runtime/runtime.c:73
        runtime.panicindex()
main.main+0x8d C:/GOEXCE~1/basics/DATATY~1/slice.go:9
        main.main()
runtime.mainstart+0xf 386/asm.s:93
        runtime.mainstart()
runtime.goexit /go/src/pkg/runtime/proc.c:178
        runtime.goexit()
----- goroutine created by -----
_rt0_386+0xbf 386/asm.s:80

虽然如果打印了 k[0] 或 k[1]，它运行正常。您能否解释一下容量对 slice 的确切含义。

Answer 1

你只是在索引，所以索引必须小于长度。 relevant section of the Go specification说

A primary expression of the form

a[x]

...

For a of type A or *A where A is an array type, or for a of type S where S is a slice type:

x must be an integer value and 0 <= x < len(a)

但是，如果您正在“slice ”(例如 a[6:9])，那么它将使用大于长度但在容量范围内的索引。