如何在golang中枚举？

I have

const (
  BlahFoo = 1 << iota
  MooFoo
)

then

type Cluster struct {
  a  int
  b  int
}

I want Cluster.a to only be BlahFoo or MooFoo

How do I enforce that?

type FooEnum int

const (
  BlahFoo FooEnum = 1 << iota
  MooFoo
)

type Cluster struct {
  a FooEnum
  b int
}