1/*
2 * Copyright (C) 2012 The Guava Authors
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.common.reflect;
18
19import com.google.common.annotations.Beta;
20import com.google.common.collect.ForwardingMap;
21import com.google.common.collect.ImmutableMap;
22
23import java.util.Map;
24
25/**
26 * A type-to-instance map backed by an {@link ImmutableMap}. See also {@link
27 * MutableTypeToInstanceMap}.
28 *
29 * @author Ben Yu
30 * @since 13.0
31 */
32@Beta
33public final class ImmutableTypeToInstanceMap<B> extends ForwardingMap<TypeToken<? extends B>, B>
34    implements TypeToInstanceMap<B> {
35
36  /** Returns an empty type to instance map. */
37  public static <B> ImmutableTypeToInstanceMap<B> of() {
38    return new ImmutableTypeToInstanceMap<B>(ImmutableMap.<TypeToken<? extends B>, B>of());
39  }
40
41  /** Returns a new builder. */
42  public static <B> Builder<B> builder() {
43    return new Builder<B>();
44  }
45
46  /**
47   * A builder for creating immutable type-to-instance maps. Example:
48   * <pre>   {@code
49   *
50   *   static final ImmutableTypeToInstanceMap<Handler<?>> HANDLERS =
51   *       ImmutableTypeToInstanceMap.<Handler<?>>builder()
52   *           .put(new TypeToken<Handler<Foo>>() {}, new FooHandler())
53   *           .put(new TypeToken<Handler<Bar>>() {}, new SubBarHandler())
54   *           .build();}</pre>
55   *
56   * <p>After invoking {@link #build()} it is still possible to add more entries
57   * and build again. Thus each map generated by this builder will be a superset
58   * of any map generated before it.
59   *
60   * @since 13.0
61   */
62  @Beta
63  public static final class Builder<B> {
64    private final ImmutableMap.Builder<TypeToken<? extends B>, B> mapBuilder
65        = ImmutableMap.builder();
66
67    private Builder() {}
68
69    /**
70     * Associates {@code key} with {@code value} in the built map. Duplicate
71     * keys are not allowed, and will cause {@link #build} to fail.
72     */
73    public <T extends B> Builder<B> put(Class<T> key, T value) {
74      mapBuilder.put(TypeToken.of(key), value);
75      return this;
76    }
77
78    /**
79     * Associates {@code key} with {@code value} in the built map. Duplicate
80     * keys are not allowed, and will cause {@link #build} to fail.
81     */
82    public <T extends B> Builder<B> put(TypeToken<T> key, T value) {
83      mapBuilder.put(key.rejectTypeVariables(), value);
84      return this;
85    }
86
87    /**
88     * Returns a new immutable type-to-instance map containing the entries
89     * provided to this builder.
90     *
91     * @throws IllegalArgumentException if duplicate keys were added
92     */
93    public ImmutableTypeToInstanceMap<B> build() {
94      return new ImmutableTypeToInstanceMap<B>(mapBuilder.build());
95    }
96  }
97
98  private final ImmutableMap<TypeToken<? extends B>, B> delegate;
99
100  private ImmutableTypeToInstanceMap(ImmutableMap<TypeToken<? extends B>, B> delegate) {
101    this.delegate = delegate;
102  }
103
104  @Override public <T extends B> T getInstance(TypeToken<T> type) {
105    return trustedGet(type.rejectTypeVariables());
106  }
107
108  /**
109   * Guaranteed to throw an exception and leave the map unmodified.
110   *
111   * @throws UnsupportedOperationException always
112   */
113  @Override public <T extends B> T putInstance(TypeToken<T> type, T value) {
114    throw new UnsupportedOperationException();
115  }
116
117  @Override public <T extends B> T getInstance(Class<T> type) {
118    return trustedGet(TypeToken.of(type));
119  }
120
121  /**
122   * Guaranteed to throw an exception and leave the map unmodified.
123   *
124   * @throws UnsupportedOperationException always
125   */
126  @Override public <T extends B> T putInstance(Class<T> type, T value) {
127    throw new UnsupportedOperationException();
128  }
129
130  @Override protected Map<TypeToken<? extends B>, B> delegate() {
131    return delegate;
132  }
133
134  @SuppressWarnings("unchecked") // value could not get in if not a T
135  private <T extends B> T trustedGet(TypeToken<T> type) {
136    return (T) delegate.get(type);
137  }
138}
139