Function init

internal/spew/bypass.go:106–146

Sanity checks against future reflect package changes to the type or semantics of the Value.flag field.

()

// Sanity checks against future reflect package changes
// to the type or semantics of the Value.flag field.
func init() {
	field, ok := reflect.TypeOf(reflect.Value{}).FieldByName("flag")
	if !ok {
		panic("reflect.Value has no flag field")
	}
	if field.Type.Kind() != reflect.TypeOf(flag(0)).Kind() {
		panic("reflect.Value flag field has changed kind")
	}
	type t0 int
	var t struct {
		A t0
		// t0 will have flagEmbedRO set.
		t0
		// a will have flagStickyRO set
		a t0
	}
	vA := reflect.ValueOf(t).FieldByName("A")
	va := reflect.ValueOf(t).FieldByName("a")
	vt0 := reflect.ValueOf(t).FieldByName("t0")

	// Infer flagRO from the difference between the flags
	// for the (otherwise identical) fields in t.
	flagPublic := *flagField(&vA)
	flagWithRO := *flagField(&va) | *flagField(&vt0)
	flagRO = flagPublic ^ flagWithRO

	// Infer flagAddr from the difference between a value
	// taken from a pointer and not.
	vPtrA := reflect.ValueOf(&t).Elem().FieldByName("A")
	flagNoPtr := *flagField(&vA)
	flagPtr := *flagField(&vPtrA)
	flagAddr = flagNoPtr ^ flagPtr

	// Check that the inferred flags tally with one of the known versions.
	for _, f := range okFlags {
		if flagRO == f.ro && flagAddr == f.addr {
			return
		}
	}
	panic("reflect.Value read-only flag has changed semantics")
}