arrays - 如何在不更改原始数组的情况下复制数组？

Question

我想复制一个数组，但复制的数组也总是对原始数组进行更改。为什么会这样？
以下是该问题的代码示例:

package main

import (
    "fmt"
)

func main() {
    array := make([]int, 2)
    for i := range array {
        array[i] = 0
    }

    oldArray := array
    array[0] = 3 // why does this also change oldArray?
    oldArray[1] = 2 // why does this also change the original array?

    fmt.Println(oldArray, array)
    // I expected [0,2], [3,0]
    // but it returns [3,2], [3,2]

}

我试图启动变量 oldArray之前 array但结果是一样的。

Answer 1

在您的示例代码中，您正在使用 slices ，不是 arrays .
从 slice 文档:

A slice is a descriptor for a contiguous segment of an underlying array and provides access to a numbered sequence of elements from that array.

当您将 slice 分配给变量时，您正在创建该描述符的副本，因此处理相同的底层数组。当您实际使用数组时，它具有您期望的行为。
slice 文档中的另一个片段(重点是我的):

A slice, once initialized, is always associated with an underlying array that holds its elements. A slice therefore shares storage with its array and with other slices of the same array; by contrast, distinct arrays always represent distinct storage.

这是一个代码示例(对于 slice ，第一个元素的内存地址在括号中，以明确指出两个 slice 何时使用相同的底层数组):

package main

import (
    "fmt"
)

func main() {
    // Arrays
    var array [2]int
    newArray := array
    array[0] = 3
    newArray[1] = 2
    fmt.Printf("Arrays:\narray: %v\nnewArray: %v\n\n", array, newArray)

    // Slices (using copy())
    slice := make([]int, 2)
    newSlice := make([]int, len(slice))
    copy(newSlice, slice)
    slice[0] = 3
    newSlice[1] = 2
    fmt.Printf("Slices (different arrays):\nslice (%p): %v \nnewSlice (%p): %v\n\n", slice, slice, newSlice, newSlice)

    // Slices (same underlying array)
    slice2 := make([]int, 2)
    newSlice2 := slice2
    slice2[0] = 3
    newSlice2[1] = 2
    fmt.Printf("Slices (same array):\nslice2 (%p): %v \nnewSlice2 (%p): %v\n\n", slice2, slice2, newSlice2, newSlice2)
}

输出:

Arrays:
array: [3 0]
newArray: [0 2]

Slices (different arrays):
slice (0xc000100040): [3 0] 
newSlice (0xc000100050): [0 2]

Slices (same array):
slice2 (0xc000100080): [3 2] 
newSlice2 (0xc000100080): [3 2]

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