How do you model enums in Go with iota? How do you add String() via go generate stringer, validate values, and handle the zero value?

Define a named integer type and a const block that uses iota. Go does not have closed enums: Status(42) compiles, and untyped constants convert implicitly, so validation has to be explicit.

//go:generate go run golang.org/x/tools/cmd/stringer -type=Status -trimprefix=Status
type Status int

const (
	StatusUnknown   Status = iota // 0: zero value means "not set"
	StatusActive                  // 1
	StatusSuspended               // 2
	statusEnd                     // sentinel for range checks, unexported
)

func (s Status) Valid() bool { return s > StatusUnknown && s < statusEnd }

func (s Status) MarshalText() ([]byte, error) {
	if !s.Valid() {
		return nil, fmt.Errorf("invalid status %d", int(s))
	}
	return []byte(s.String()), nil
}

Running go generate ./... writes status_string.go. The generated file includes a compile-time guard that fails to build if the constant values change without regenerating, and it prints Status(42) for unknown values. Zero value: make 0 mean "Unknown/Invalid" so that an uninitialized struct field or a missing JSON field is detectable. Otherwise a zero-valued struct silently gets your first real state. Use iota + 1 or _ = iota to skip it. Gotchas: never persist iota values to a DB or the wire and then reorder constants. Store strings, or give the numbers explicit values. For bit flags use 1 << iota. Add UnmarshalText that rejects unknown names so the check also runs at system boundaries.