重新切片切片Golang [英] Re-slicing slices in Golang

问题描述

我最近有回暖的围棋，现在我用下面的code困惑：

I recently has pick up the Go, and now I confused with the following code:

package main

import "fmt"

func main() {
    a := make([]int, 5)
    printSlice("a", a)
    b := make([]int, 0, 5)
    printSlice("b", b)
    c := b[:2]
    printSlice("c", c)
    d := c[2:5]
    printSlice("d", d)
}

func printSlice(s string, x []int) {
    fmt.Printf("%s len=%d cap=%d %v\n",
        s, len(x), cap(x), x)
}

和结果：

a len=5 cap=5 [0 0 0 0 0]
b len=0 cap=5 []
c len=2 cap=5 [0 0] //why the capacity of c not 2 but 5 instead
d len=3 cap=3 [0 0 0]

任何帮助将感谢。

Any help would thanks.

推荐答案

C 是从阵列中采取了分片 B 。这不是一个拷贝，而只是一个窗口超过的2第一元素中，b 。

c is a slice taken from the array b. This isn't a copy, but just a window over the 2 first elements of b.

由于 B 拥有5的容量， C 可以扩展到取3其他地方（其实它使一个新的片但在内存中的同一个地方）。

As b has a capacity of 5, c could be extended to take the 3 other places (in fact it makes a new slice but over the same place in memory).

片的最大容量是底层阵列的容量减去所述阵列中的片的起点的位置：

The maximal capacity of the slice is the capacity of the underlying array minus the position of the start of the slice in the array :

 array : [0 0 0 0 0 0 0 0 0 0 0 0]
 array :  <----   capacity   --->
 slice :     [0 0 0 0]
 slice :      <---- capacity ---> 

也许这一计划将使其更清楚，C和D都只是窗户乙级以上：

Maybe this program will make it more clear that c and d are just windows over b :

func main() {
    b := make([]int, 0, 5)
    c := b[:2]
    d := c[1:5] // this is equivalent to d := b[1:5]
    d[0] = 1
    printSlice("c", c)
    printSlice("d", d)
}

输出：

c len=2 cap=5 [0 1] // modifying d has modified c
d len=4 cap=4 [1 0 0 0] 

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