Change from []Struct to []Interface in go

array_change.go

package main

type Box interface {
	Width() int
}

type Square struct {
	w int
}

func (sq Square) Width() int {
	return sq.w
}

func GraphGen() []Square {
	sqs := make([]Square, 5)
	for i:=0; i<5; i++ {
		sqs[i] = Square{i}
	}
	return sqs
}

/*
 Would like to be able to pass an array []Square in here
*/
func PrintBoxes(sqs []Box) {
	for i:=0; i< len(sqs); i++ {
		PrintBox(sqs[i])
	}
}

func PrintBox(sq Box) {
	println(sq.Width())
}

func main() {
	sqs := GraphGen()
	bxs := make([]Box, len(sqs))
	copy(sqs[:], bxs[:])
	for bx := range bxs {
		println(bx)
	}
	//PrintBoxes(sqs) // fails to compile because []Box is not the same as []Square
}