// errLessData - returned when less data available than what was requested.
var errLessData = StorageErr("less data available than what was requested")

// errMoreData = returned when more data was sent by the caller than what it was supposed to.
var errMoreData = StorageErr("more data was sent than what was advertised")

// indicates readDirFn to return without further applying the fn()
var errDoneForNow = errors.New("done for now")

// An Update function must be set to provide an updated value when needed.
type Cache[T any] struct {
	// updateFn must return an updated value.
	// If an error is returned the cached value is not set.
	// Only one caller will call this function at any time, others will be blocking.
	// The returned value can no longer be modified once returned.
	// Should be set before calling Get().
	updateFn func() (T, error)

	// ttl for a cached value.