// update function, making it ready for use.
func NewFromFunc[T any](ttl time.Duration, opts Opts, update func() (T, error)) *Cache[T] {
	return &Cache[T]{
		ttl:      ttl,
		updateFn: update,
		opts:     opts,
	}
}

// InitOnce initializes the cache with a TTL and an update function. It is
// guaranteed to be called only once.
func (t *Cache[T]) InitOnce(ttl time.Duration, opts Opts, update func() (T, error)) {
	t.Once.Do(func() {

	}
}

func saveKeyEtcdWithTTL(ctx context.Context, client *etcd.Client, key string, data []byte, ttl int64) error {
	timeoutCtx, cancel := context.WithTimeout(ctx, defaultContextTimeout)
	defer cancel()
	lease, err := client.Grant(timeoutCtx, ttl)
	if err != nil {
		return etcdErrToErr(err, client.Endpoints())
	}
	_, err = client.Put(timeoutCtx, key, string(data), etcd.WithLease(lease.ID))