// 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.

	if err != nil {
		return nil, err
	}

	resp, err := c.clnt.Do(req)
	if err != nil {
		return nil, err
	}
	defer xhttp.DrainBody(resp.Body)

	switch resp.StatusCode {
	case http.StatusNotFound:
		return nil, ErrKeyMissing
	case http.StatusOK:
		co := &ObjectInfo{}
		return co, co.DecodeMsg(msgp.NewReader(resp.Body))
	default:
		return nil, ErrInvalidArgument
	}
}