code: func (c *ExpirationCache) Delete(obj interface{}) error {
  	key, err := c.keyFunc(obj)
  	if err != nil {
  		return KeyError{obj, err}
  	}
  	c.expirationLock.Lock()
  	defer c.expirationLock.Unlock()
  	c.cacheStorage.Delete(key)
  	return nil
  }
docs: // Delete removes an item from the cache.