为什么在 go editing slice inside 函数中不应用长度更新？

Fast response: because a slice is only a reference to the original array

正如你在下面的例子中看到的，我有一个 slice ，它的值将被外部函数修改，但是追加操作被完全忽略，直到你从函数返回值并将其重新分配给原始 slice .

Working to improve the examples, I've added function that pass by reference and make modification operations to increase comfort about the solutions

package main

import (
    "fmt"

)
var sli = make([]int,8)

func main() {

    fmt.Println("START STATUS_____")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))

    editSli(sli)
    fmt.Println("EDIT RESULT STATUS_____")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))


    sli = updateSli(sli)
    fmt.Println("UPDATE RESULT STATUS_____")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))

    sli = append(sli, 15, 16, 17)
    fmt.Println("DIRECT APPEND RESULT STATUS_____")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))

    sli[13] = 99
    fmt.Println("DIRECT ASSIGNMENT OF LAST ELEMENT (13°) STATUS_____")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))

    updateSliPointer(&sli)
    fmt.Println("\n*** Finally, passing the slice as a pointer will modify the sctructure: ")
    fmt.Println("slice",sli)
    fmt.Println("   cap:", cap(sli))
    fmt.Println("   len:", len(sli))
}

func editSli(sliOrigin []int) {
    sliOrigin[7] = 11
    sliOrigin = append(sliOrigin, 33, 34, 35) //don't work
    fmt.Println("\ninside the edit Slice function the sli is =", sliOrigin)
    fmt.Println("and the direct assignment of the last element (7°) ar right working.")
    fmt.Println("However, the slice append will not be applied to the original slice because this is an internal copy")
}

func updateSli(sliOrigin []int) []int{
    sliOrigin = append(sliOrigin, 12, 13, 14) //it works!
    fmt.Println("\ninside the update Slice function the sli is = ", sliOrigin)
    fmt.Println("and this append will be applied to the original one becouse of the return value of this function is a new slice")
    return sliOrigin
}

func updateSliPointer(sliOrigin *[]int) {
    //don't work *sliOrigin[7] = 11
    *sliOrigin = append(*sliOrigin, 100, 101, 102)
    fmt.Println("\ninside the UPDATE Slice POINTER function we have a sli pointer and we can modify directly the structures appending elements =", sliOrigin)
    fmt.Println("\nbut to access the values and modify it we have to create a local instance")
    var x = *sliOrigin
    x[4] = 9
}

运行它会产生:

START STATUS_____
slice [0 0 0 0 0 0 0 0]
    cap: 8
    len: 8

inside the edit Slice function the sli is = [0 0 0 0 0 0 0 11 33 34 35]
and the direct assignment of the last element (7°) ar right working.

However, the slice append will not be applied to the original slice because this is an internal copy
EDIT RESULT STATUS_____
    slice [0 0 0 0 0 0 0 11]
    cap: 8
    len: 8

inside the update Slice function the sli is =  [0 0 0 0 0 0 0 11 12 13 14]
and this append will be applied to the original one becouse of the return value of this function is a         new slice
UPDATE RESULT STATUS_____
    slice [0 0 0 0 0 0 0 11 12 13 14]
    cap: 16
    len: 11
DIRECT APPEND RESULT STATUS_____
    slice [0 0 0 0 0 0 0 11 12 13 14 15 16 17]
    cap: 16
    len: 14
DIRECT ASSIGNMENT OF LAST ELEMENT (13°) STATUS_____
    slice [0 0 0 0 0 0 0 11 12 13 14 15 16 99]
    cap: 16
    len: 14

inside the UPDATE Slice POINTER function we have a sli pointer and we can modify directly the         structures appending elements = &[0 0 0 0 0 0 0 11 12 13 14 15 16 99 100 101 102]

but to access the values and modify it we have to create a local instance

*** Finally, passing the slice as a pointer will modify the sctructure: 
    slice [0 0 0 0 9 0 0 11 12 13 14 15 16 99 100 101 102]
    cap: 32
    len: 17