quiver/lib/src/cache/cache.dart

// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

part of quiver.cache;

/**
 * A function that produces a value for [key], for when a [Cache] needs to
 * populate an entry.
 *
 * The loader function should either return a value synchronously or a [Future]
 * which completes with the value asynchronously.
 */
typedef dynamic Loader<K>(K key);

/**
 * A semi-persistent mapping of keys to values.
 *
 * All access to a Cache is asynchronous because many implementations will store
 * their entries in remote systems, isolates, or otherwise have to do async IO
 * to read and write.
 */
abstract class Cache<K, V> {

  /**
   * Returns the value associated with [key].
   */
  Future<V> get(K key, {Loader<K> ifAbsent});

  /**
   * Sets the value associated with [key]. The Future completes with null when
   * the operation is complete.
   */
  Future set(K key, V value);

  /**
   * Removes the value associated with [key]. The Future completes with null
   * when the operation is complete.
   */
  Future invalidate(K key);
}