附加到切片的多个实例

Question

If I have two pointers to slices s1, s2, which initially point to the same slice, is it possible to append to one of the slices and have the other slice also point to the updated slice? This seems to be a problem because, appending to slices might make a new slice with the entries copied over if the capacity is insufficient.

The following is a slightly complicated version on the Go Playground that is closer to my use case. Namely, I have nodes that have a pointer to a (global) queue which is implemented by a slice. When one node updates the global queue, I want that to be reflected in the slice that the other node points to.

https://play.golang.org/p/NG11HbLBrI

Answer 1

Add a indirect layer, i.e. a pointer, can help you work this out https://play.golang.org/p/R7JILCbYTF

package main

import (
    "fmt"
)

type queue *[]int

type node struct {
    id int
    list *queue
}

func (n *node) mutate(){
    newSlice := append(**n.list, 1)
    *n.list = &newSlice
}
func (n *node) get(idx int) int{
    return (*(*[]int)(*n.list))[idx]
}

func main() {
    /* Make empty queue */
    s:=make([]int, 0)
    q1:=queue(&s)
    fmt.Println(q1)

    /* Make new nodes */
    n1 := new(node)
    n1.id = 0
    n1.list = &q1
    fmt.Println(n1)

    n2 := new(node)
    n2.id = 1
    n2.list = n1.list
    fmt.Println(n2)

    /* Mutate node in n1 */
    n1.mutate()
    fmt.Println(n1, n2) // n1.list != n2.list
    fmt.Println(n1.list, n2.list)
    fmt.Println(n1.get(0))
    n2.mutate()
    fmt.Println(n2.get(0))
}