interface KeyValueStoreInterface

interface KeyValueStoreInterface {
    
    /**
     * Returns the name of this collection.
     *
     * @return string
     *   The name of this collection.
     */
    public function getCollectionName();
    
    /**
     * Returns whether a given key exists in the store.
     *
     * @param string $key
     *   The key to check.
     *
     * @return bool
     *   TRUE if the key exists, FALSE otherwise.
     */
    public function has($key);
    
    /**
     * Returns the stored value for a given key.
     *
     * @param string $key
     *   The key of the data to retrieve.
     * @param mixed $default
     *   The default value to use if the key is not found.
     *
     * @return mixed
     *   The stored value, or the default value if no value exists.
     */
    public function get($key, $default = NULL);
    
    /**
     * Returns the stored key/value pairs for a given set of keys.
     *
     * @param array $keys
     *   A list of keys to retrieve.
     *
     * @return array
     *   An associative array of items successfully returned, indexed by key.
     *
     * @todo Determine the best return value for non-existing keys in
     *   https://www.drupal.org/node/2787737
     */
    public function getMultiple(array $keys);
    
    /**
     * Returns all stored key/value pairs in the collection.
     *
     * @return array
     *   An associative array containing all stored items in the collection.
     */
    public function getAll();
    
    /**
     * Saves a value for a given key.
     *
     * @param string $key
     *   The key of the data to store.
     * @param mixed $value
     *   The data to store.
     */
    public function set($key, $value);
    
    /**
     * Saves a value for a given key if it does not exist yet.
     *
     * @param string $key
     *   The key of the data to store.
     * @param mixed $value
     *   The data to store.
     *
     * @return bool
     *   TRUE if the data was set, FALSE if it already existed.
     */
    public function setIfNotExists($key, $value);
    
    /**
     * Saves key/value pairs.
     *
     * @param array $data
     *   An associative array of key/value pairs.
     */
    public function setMultiple(array $data);
    
    /**
     * Renames a key.
     *
     * @param string $key
     *   The key to rename.
     * @param string $new_key
     *   The new key name.
     */
    public function rename($key, $new_key);
    
    /**
     * Deletes an item from the key/value store.
     *
     * @param string $key
     *   The item name to delete.
     */
    public function delete($key);
    
    /**
     * Deletes multiple items from the key/value store.
     *
     * @param array $keys
     *   A list of item names to delete.
     */
    public function deleteMultiple(array $keys);
    
    /**
     * Deletes all items from the key/value store.
     */
    public function deleteAll();

}