1/**
2 * Copyright (C) 2006 Google Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.inject;
18
19/**
20 * A scope is a level of visibility that instances provided by Guice may have.
21 * By default, an instance created by the {@link Injector} has <i>no scope</i>,
22 * meaning it has no state from the framework's perspective -- the
23 * {@code Injector} creates it, injects it once into the class that required it,
24 * and then immediately forgets it. Associating a scope with a particular
25 * binding allows the created instance to be "remembered" and possibly used
26 * again for other injections.
27 *
28 * <p>An example of a scope is {@link Scopes#SINGLETON}.
29 *
30 * @author crazybob@google.com (Bob Lee)
31 */
32public interface Scope {
33
34  /**
35   * Scopes a provider. The returned provider returns objects from this scope.
36   * If an object does not exist in this scope, the provider can use the given
37   * unscoped provider to retrieve one.
38   *
39   * <p>Scope implementations are strongly encouraged to override
40   * {@link Object#toString} in the returned provider and include the backing
41   * provider's {@code toString()} output.
42   *
43   * @param key binding key
44   * @param unscoped locates an instance when one doesn't already exist in this
45   *  scope.
46   * @return a new provider which only delegates to the given unscoped provider
47   *  when an instance of the requested object doesn't already exist in this
48   *  scope
49   */
50  public <T> Provider<T> scope(Key<T> key, Provider<T> unscoped);
51
52  /**
53   * A short but useful description of this scope.  For comparison, the standard
54   * scopes that ship with guice use the descriptions
55   * {@code "Scopes.SINGLETON"}, {@code "ServletScopes.SESSION"} and
56   * {@code "ServletScopes.REQUEST"}.
57   */
58  String toString();
59}
60