https://www.v2ex.com/t/649712

wrEB.go

package main

import (
	"fmt"
)

func test(a []int) {
	a = append(a, 4)
}

func main() {
	s := make([]int, 3, 4)
	s[0] = 1
	s[1] = 2
	s[2] = 3
	fmt.Println(s) //[1 2 3]
	test(s)
	s = s[:4]
	fmt.Println(s) //[1 2 3 4]
}