代码

func main () {
    copyForSlice()
}

func copyForSlice() {
    xishuName := make([]string,3)
    xishuName[0] = "刘备"
    xishuName[1] = "关羽"
    xishuName[2] = "张飞"
    dongwuName := make([]string,3)
    dongwuName[0] = "孙权"
    dongwuName[1] = "周瑜"
    copy(dongwuName,xishuName)
    fmt.Println(dongwuName)
}

结果

三个成员的切片 copy到两个成员的切片，目标切片变成三个成员。
反过来也是一样，他不会管目标切片是多少成员，都是保持源切片成员。