// updater returns an object to cache.
func NewObjectCache(f func() (interface{}, error), ttl time.Duration) *ObjectCache {
	return &ObjectCache{
		updater: f,
		cache:   expirationcache.NewTTLStore(stringKeyFunc, ttl),
	}
}

// stringKeyFunc is a string as cache key function
func stringKeyFunc(obj interface{}) (string, error) {
	key := obj.(objectEntry).key
	return key, nil
}