如何在接口声明[golang]中扩展数组？

i have this function declaration and i want return array of interface.
spread(1,2,3) => [4,5,6].
i also searched any place like play.golang,other stackoverflow go tags but nothing found

func spread2(a ...interface{}) []interface{} {
        a:=[]int{4,5,6}
        return []interface{}{a}//[[4,5,6]] NO

        return []interface{}{a...} //[4,5,6] YES,i want this; 
                                   //but got error
}

the error i got is : syntax error: unexpected ..., expecting comma or }

in my case []interface{} input is same as output.
so just return any thing as array is ok

For example,

package main

import (
    "fmt"
)

func spread(a ...interface{}) []interface{} {
    return a
}

func main() {
    fmt.Println(spread(1, 2, 3))
}

Playground: https://play.golang.org/p/Bqgu_A1BCti

Output:

[1 2 3]

An optimizing compiler may inline the spread function.