optional.h revision e62f9949c5aa827e175cfb239d9840d7517e8052 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
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
17#ifndef UTIL_CHRE_OPTIONAL_H_
18#define UTIL_CHRE_OPTIONAL_H_
19
20namespace chre {
21
22/**
23 * This container keeps track of an optional object. The container is similar to
24 * std::optional introduced in C++17.
25 */
26template<typename ObjectType>
27class Optional {
28 public:
29  /**
30   * Default constructs the optional object with no initial value.
31   */
32  Optional();
33
34  /**
35   * Constructs an optional instance with an initial value.
36   *
37   * @param object The initial value of the object.
38   */
39  Optional(const ObjectType& object);
40
41  /**
42   * Constructs an optional instance with an initial value by moving it.
43   *
44   * @param object The instance of the initial object to take ownership of.
45   */
46  Optional(ObjectType&& object);
47
48  /**
49   * @return Returns true if the object tracked by this container has been
50   * assigned.
51   */
52  bool has_value() const;
53
54  /**
55   * Resets the optional container by invoking the destructor on the underlying
56   * object.
57   */
58  void reset();
59
60  /**
61   * Performs a move assignment operation to the underlying object managed by
62   * this container.
63   *
64   * @param other The other object to move from.
65   * @return Returns a reference to this object.
66   */
67  Optional<ObjectType>& operator=(ObjectType&& other);
68
69  /**
70   * Performs a move assignment from one optional to another. The other is left
71   * in a state with no value.
72   *
73   * @param other The other object to move.
74   * @return Returns a reference to this object.
75   */
76  Optional<ObjectType>& operator=(Optional<ObjectType>&& other);
77
78  /**
79   * Performs a copy assignment operation to the underlying object managed by
80   * this container.
81   *
82   * @param other The other object to copy from.
83   * @return Returns a reference to this object.
84   */
85  Optional<ObjectType>& operator=(const ObjectType& other);
86
87  /**
88   * Performs a copy assignment from one optional to another.
89   *
90   * @param other The other object to copy.
91   * @return Returns a reference to this object.
92   */
93  Optional<ObjectType>& operator=(const Optional<ObjectType>& other);
94
95  /**
96   * Obtains a reference to the underlying object managed by this container.
97   * The behavior of this is undefined if has_value() returns false.
98   *
99   * @return Returns a reference to the underlying object tracked by this
100   *         container.
101   */
102  ObjectType& operator*();
103
104  /**
105   * Obtains a const reference to the underlying object managed by this
106   * container. The behavior of this is undefined if has_value() returns false.
107   *
108   * @return Returns a const reference to the underlying object tracked by this
109   *         container.
110   */
111  const ObjectType& operator*() const;
112
113  /**
114   * Obtains a pointer to the underlying object managed by this container. The
115   * object may not be well-formed if has_value() returns false.
116   *
117   * @return Returns a pointer to the underlying object tracked by this
118   *         container.
119   */
120  ObjectType *operator->();
121
122  /**
123   * Obtains a const pointer to the underlying object managed by this container.
124   * The object may not be well-formed if has_value() returns false.
125   *
126   * @return Returns a const pointer to the underlying object tracked by this
127   *         container.
128   */
129  const ObjectType *operator->() const;
130
131 private:
132  //! The optional object being tracked by this container.
133  ObjectType mObject;
134
135  //! Whether or not the object is set.
136  bool mHasValue = false;
137};
138
139}  // namespace chre
140
141#include "chre/util/optional_impl.h"
142
143#endif  // UTIL_CHRE_OPTIONAL_H_
144