如何将切片复制到自身

Question

What I mean is, for example

arr := []int{1, 2, 3}
arr = copy(arr, arr)
fmt.Println(arr) // Expectation: [1, 2, 3, 1, 2, 3] Reality: [1, 2, 3]

I also tried

for _, el := range(arr) {
    arr = append(arr, el)
}

None of these work.

Answer 1

Use arr = append(arr, arr...) , try this :

package main

import "fmt"

func main() {
    arr := []int{1, 2, 3}
    arr = append(arr, arr...)
    fmt.Println(arr)
}

Output:

[1 2 3 1 2 3]