向外扩展切片和底层数组

Question

我有一个数组和一个指向它的切片，如下所示：

package main

import "fmt"

func main() {

    array_str := []string{"0a","1b","2c","3d","4e"}
    slice_str:=array_str[1:4]
    fmt.Println("Initially :")
    fmt.Println("Printing 1 :Array :",array_str)
    fmt.Println("Printing 1 :Slice:",slice_str)

    //Step 1.Changing Slice and it get reflected in array
    fmt.Println("\nAfter Alteration:")
    slice_str[0]="alterd_1b"
    fmt.Println("Printing 2 :Array :",array_str)
    fmt.Println("Printing 2 :Slice:",slice_str)
    fmt.Println("len of  slice_str:",len(slice_str)," cap of         slice_str:",cap(slice_str),"len of  array_str:",len(array_str))

    //Step 2.appending to slice and it get reflected

    slice_str = append(slice_str,"apnded_elemnt")
    fmt.Println("\nAfter Apending:")
    fmt.Println("Printing 3 :Array :",array_str)//"4e" is replaced with "apnded_elemnt" in array !!
    fmt.Println("Printing 3 :Slice:",slice_str)
    fmt.Println("len of  slice_str:",len(slice_str)," cap of   slice_str:",cap(slice_str),"len of  array_str:",len(array_str))

    //Step 3.Again appending to slice so that lentght of slice is growing further to  underlaying array
    slice_str = append(slice_str,"outgrown_elemnt")
    fmt.Println("\nAfter OUT GROWING:")
    fmt.Println("Printing 4 :Array :",array_str)//obeviously out grown elemnt not added to array that is fine
    fmt.Println("Printing 4 :Slice:",slice_str)
    fmt.Println("len of  slice_str:",len(slice_str)," cap of slice_str:",cap(slice_str),"len of  array_str:",len(array_str))
    //How Capacity Become 8 here ???

    //Step 4 .Now Changing Slice element which is in Range of array to verify it reflect on array:
    fmt.Println("\nAfter Post out grown Alteration:")
    slice_str[0]="again_alterd_1b"
    fmt.Println("Printing 2 :Array :",array_str)//Change in slice is not reflectd in array .Why ?
    fmt.Println("Printing 2 :Slice:",slice_str)
}

游乐场：http：//play.golang.org/p/3z52HXHQ7s

问题：

1. 在第3步中，为什么cap切片从4跳到8？

2. 在第4步中：超出切片的范围后，对切片元素的更改（不在数组范围内）不会反映到数组，反之亦然。它长大后为什么没有发生？当切片长大时实际发生什么？

Answer 1

看到这里：http : //blog.golang.org/slices

简短的答案：1）它通过加倍（简短）而增长。如果追加一次，则也可能会第二次追加，这样可以避免分配。2）这就是切片生长的工作方式。数组无法增长，因此将分配一个新的更大的数组，复制旧的数组，然后您将得到一个指向更大副本的切片。

（golang.org网站上的文档确实很有帮助，可读，简短，准确。我建议您先问一下golang.org，然后再问这里。）