golang – how to initialize a map field within a struct?

I would probably use a constructor to do this:

func NewGraph() *Graph {
    var g Graph
    g.connections = make(map[Vertex][]Vertex)
    return &g
}

I’ve found this example in the standard image/jpeg package (not with a map though, but with a slice):

type Alpha struct {
    Pix []uint8
    Stride int
    Rect Rectangle
}

func NewAlpha(r Rectangle) *Alpha {
    w, h := r.Dx(), r.Dy()
    pix := make([]uint8, 1*w*h)
    return &Alpha{pix, 1 * w, r}
}