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platform/NonCopyable.h@172:65be27845400, 2019-02-20 (annotated)
- Committer:
- AnnaBridge
- Date:
- Wed Feb 20 20:53:29 2019 +0000
- Revision:
- 172:65be27845400
- Parent:
- 171:3a7713b1edbc
mbed library release version 165
Who changed what in which revision?
User | Revision | Line number | New contents of line |
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AnnaBridge | 146:22da6e220af6 | 1 | /* Copyright (c) 2017 ARM Limited |
AnnaBridge | 172:65be27845400 | 2 | * SPDX-License-Identifier: Apache-2.0 |
AnnaBridge | 146:22da6e220af6 | 3 | * |
AnnaBridge | 146:22da6e220af6 | 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
AnnaBridge | 146:22da6e220af6 | 5 | * you may not use this file except in compliance with the License. |
AnnaBridge | 146:22da6e220af6 | 6 | * You may obtain a copy of the License at |
AnnaBridge | 146:22da6e220af6 | 7 | * |
AnnaBridge | 146:22da6e220af6 | 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
AnnaBridge | 146:22da6e220af6 | 9 | * |
AnnaBridge | 146:22da6e220af6 | 10 | * Unless required by applicable law or agreed to in writing, software |
AnnaBridge | 146:22da6e220af6 | 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
AnnaBridge | 146:22da6e220af6 | 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
AnnaBridge | 146:22da6e220af6 | 13 | * See the License for the specific language governing permissions and |
AnnaBridge | 146:22da6e220af6 | 14 | * limitations under the License. |
AnnaBridge | 146:22da6e220af6 | 15 | */ |
AnnaBridge | 146:22da6e220af6 | 16 | |
AnnaBridge | 146:22da6e220af6 | 17 | #ifndef MBED_NONCOPYABLE_H_ |
AnnaBridge | 146:22da6e220af6 | 18 | #define MBED_NONCOPYABLE_H_ |
AnnaBridge | 146:22da6e220af6 | 19 | |
Anna Bridge |
160:5571c4ff569f | 20 | #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) |
Anna Bridge |
160:5571c4ff569f | 21 | #include "mbed_toolchain.h" |
Anna Bridge |
160:5571c4ff569f | 22 | #include "mbed_debug.h" |
Anna Bridge |
160:5571c4ff569f | 23 | #endif |
Anna Bridge |
160:5571c4ff569f | 24 | |
Anna Bridge |
160:5571c4ff569f | 25 | namespace mbed { |
AnnaBridge | 146:22da6e220af6 | 26 | |
AnnaBridge | 171:3a7713b1edbc | 27 | /** \addtogroup platform */ |
AnnaBridge | 171:3a7713b1edbc | 28 | /** @{*/ |
AnnaBridge | 146:22da6e220af6 | 29 | /** |
AnnaBridge | 171:3a7713b1edbc | 30 | * \defgroup platform_NonCopyable NonCopyable class |
AnnaBridge | 171:3a7713b1edbc | 31 | * @{ |
AnnaBridge | 171:3a7713b1edbc | 32 | */ |
AnnaBridge | 171:3a7713b1edbc | 33 | |
AnnaBridge | 171:3a7713b1edbc | 34 | /** |
AnnaBridge | 172:65be27845400 | 35 | * Prevents generation of copy constructor and copy assignment operator in |
AnnaBridge | 171:3a7713b1edbc | 36 | * derived classes. |
AnnaBridge | 172:65be27845400 | 37 | * |
AnnaBridge | 171:3a7713b1edbc | 38 | * @par Usage |
AnnaBridge | 172:65be27845400 | 39 | * |
AnnaBridge | 172:65be27845400 | 40 | * To prevent generation of copy constructor and copy assignment operator, |
AnnaBridge | 172:65be27845400 | 41 | * inherit privately from the NonCopyable class. |
AnnaBridge | 172:65be27845400 | 42 | * |
AnnaBridge | 172:65be27845400 | 43 | * @code |
AnnaBridge | 171:3a7713b1edbc | 44 | * class Resource : NonCopyable<Resource> { }; |
AnnaBridge | 172:65be27845400 | 45 | * |
AnnaBridge | 171:3a7713b1edbc | 46 | * Resource r; |
AnnaBridge | 171:3a7713b1edbc | 47 | * // generates compile time error: |
AnnaBridge | 171:3a7713b1edbc | 48 | * Resource r2 = r; |
AnnaBridge | 171:3a7713b1edbc | 49 | * @endcode |
AnnaBridge | 172:65be27845400 | 50 | * |
AnnaBridge | 171:3a7713b1edbc | 51 | * @par Background information |
AnnaBridge | 172:65be27845400 | 52 | * |
AnnaBridge | 172:65be27845400 | 53 | * Instances of polymorphic classes are not meant to be copied. The |
AnnaBridge | 172:65be27845400 | 54 | * C++ standards generate a default copy constructor and copy assignment |
AnnaBridge | 171:3a7713b1edbc | 55 | * function if these functions have not been defined in the class. |
AnnaBridge | 172:65be27845400 | 56 | * |
AnnaBridge | 171:3a7713b1edbc | 57 | * Consider the following example: |
AnnaBridge | 172:65be27845400 | 58 | * |
AnnaBridge | 146:22da6e220af6 | 59 | * @code |
AnnaBridge | 171:3a7713b1edbc | 60 | * // base class representing a connection |
AnnaBridge | 172:65be27845400 | 61 | * struct Connection { |
AnnaBridge | 171:3a7713b1edbc | 62 | * Connection(); |
AnnaBridge | 171:3a7713b1edbc | 63 | * virtual ~Connection(); |
AnnaBridge | 171:3a7713b1edbc | 64 | * virtual void open() = 0; |
AnnaBridge | 171:3a7713b1edbc | 65 | * } |
AnnaBridge | 172:65be27845400 | 66 | * |
AnnaBridge | 172:65be27845400 | 67 | * class SerialConnection : public Connection { |
Anna Bridge |
160:5571c4ff569f | 68 | * public: |
AnnaBridge | 171:3a7713b1edbc | 69 | * SerialConnection(Serial*); |
AnnaBridge | 172:65be27845400 | 70 | * |
AnnaBridge | 146:22da6e220af6 | 71 | * private: |
AnnaBridge | 171:3a7713b1edbc | 72 | * Serial* _serial; |
AnnaBridge | 171:3a7713b1edbc | 73 | * }; |
AnnaBridge | 172:65be27845400 | 74 | * |
AnnaBridge | 172:65be27845400 | 75 | * Connection& get_connection() { |
AnnaBridge | 171:3a7713b1edbc | 76 | * static SerialConnection serial_connection; |
AnnaBridge | 171:3a7713b1edbc | 77 | * return serial_connection; |
AnnaBridge | 146:22da6e220af6 | 78 | * } |
Anna Bridge |
160:5571c4ff569f | 79 | * |
AnnaBridge | 171:3a7713b1edbc | 80 | * Connection connection = get_connection(); |
Anna Bridge |
160:5571c4ff569f | 81 | * @endcode |
AnnaBridge | 172:65be27845400 | 82 | * |
AnnaBridge | 172:65be27845400 | 83 | * There is a subtle bug in this code, the function get_connection returns a |
AnnaBridge | 172:65be27845400 | 84 | * reference to a Connection which is captured by value instead of reference. |
AnnaBridge | 172:65be27845400 | 85 | * |
AnnaBridge | 172:65be27845400 | 86 | * When `get_connection` returns a reference to serial_connection it is copied into |
AnnaBridge | 172:65be27845400 | 87 | * the local variable connection. The vtable and others members defined in Connection |
AnnaBridge | 172:65be27845400 | 88 | * are copied, but members defined in SerialConnection are left apart. This can cause |
AnnaBridge | 172:65be27845400 | 89 | * severe crashes or bugs if the virtual functions captured use members not present |
AnnaBridge | 171:3a7713b1edbc | 90 | * in the base declaration. |
AnnaBridge | 172:65be27845400 | 91 | * |
AnnaBridge | 172:65be27845400 | 92 | * To solve that problem, the copy constructor and assignment operator have to |
AnnaBridge | 172:65be27845400 | 93 | * be declared (but don't need to be defined) in the private section of the |
AnnaBridge | 171:3a7713b1edbc | 94 | * Connection class: |
AnnaBridge | 172:65be27845400 | 95 | * |
Anna Bridge |
160:5571c4ff569f | 96 | * @code |
AnnaBridge | 172:65be27845400 | 97 | * struct Connection { |
AnnaBridge | 146:22da6e220af6 | 98 | * private: |
AnnaBridge | 171:3a7713b1edbc | 99 | * Connection(const Connection&); |
AnnaBridge | 171:3a7713b1edbc | 100 | * Connection& operator=(const Connection&); |
AnnaBridge | 146:22da6e220af6 | 101 | * } |
AnnaBridge | 146:22da6e220af6 | 102 | * @endcode |
AnnaBridge | 172:65be27845400 | 103 | * |
AnnaBridge | 172:65be27845400 | 104 | * Although manually declaring private copy constructor and assignment functions |
AnnaBridge | 172:65be27845400 | 105 | * works, it is not ideal. These declarations are usually easy to forget, |
AnnaBridge | 171:3a7713b1edbc | 106 | * not immediately visible, and may be obscure to uninformed programmers. |
AnnaBridge | 172:65be27845400 | 107 | * |
AnnaBridge | 172:65be27845400 | 108 | * Using the NonCopyable class reduces the boilerplate required and expresses |
AnnaBridge | 171:3a7713b1edbc | 109 | * the intent because class inheritance appears right after the class name |
AnnaBridge | 171:3a7713b1edbc | 110 | * declaration. |
AnnaBridge | 172:65be27845400 | 111 | * |
AnnaBridge | 171:3a7713b1edbc | 112 | * @code |
AnnaBridge | 172:65be27845400 | 113 | * struct Connection : private NonCopyable<Connection> { |
AnnaBridge | 171:3a7713b1edbc | 114 | * // regular declarations |
AnnaBridge | 146:22da6e220af6 | 115 | * } |
AnnaBridge | 171:3a7713b1edbc | 116 | * @endcode |
AnnaBridge | 172:65be27845400 | 117 | * |
AnnaBridge | 172:65be27845400 | 118 | * |
AnnaBridge | 172:65be27845400 | 119 | * @par Implementation details |
AnnaBridge | 172:65be27845400 | 120 | * |
AnnaBridge | 172:65be27845400 | 121 | * Using a template type prevents cases where the empty base optimization cannot |
AnnaBridge | 172:65be27845400 | 122 | * be applied and therefore ensures that the cost of the NonCopyable semantic |
AnnaBridge | 171:3a7713b1edbc | 123 | * sugar is null. |
AnnaBridge | 172:65be27845400 | 124 | * |
Anna Bridge |
160:5571c4ff569f | 125 | * As an example, the empty base optimization is prohibited if one of the empty |
AnnaBridge | 171:3a7713b1edbc | 126 | * base classes is also a base type of the first nonstatic data member: |
Anna Bridge |
160:5571c4ff569f | 127 | * |
Anna Bridge |
160:5571c4ff569f | 128 | * @code |
AnnaBridge | 146:22da6e220af6 | 129 | * struct A { }; |
Anna Bridge |
160:5571c4ff569f | 130 | * struct B : A { |
AnnaBridge | 146:22da6e220af6 | 131 | * int foo; |
AnnaBridge | 146:22da6e220af6 | 132 | * }; |
AnnaBridge | 146:22da6e220af6 | 133 | * // thanks to empty base optimization, sizeof(B) == sizeof(int) |
Anna Bridge |
160:5571c4ff569f | 134 | * |
Anna Bridge |
160:5571c4ff569f | 135 | * struct C : A { |
AnnaBridge | 146:22da6e220af6 | 136 | * B b; |
AnnaBridge | 146:22da6e220af6 | 137 | * }; |
Anna Bridge |
160:5571c4ff569f | 138 | * |
AnnaBridge | 146:22da6e220af6 | 139 | * // empty base optimization cannot be applied here because A from C and A from |
AnnaBridge | 171:3a7713b1edbc | 140 | * // B have a different address. In that case, with the alignment |
AnnaBridge | 146:22da6e220af6 | 141 | * // sizeof(C) == 2* sizeof(int) |
AnnaBridge | 146:22da6e220af6 | 142 | * @endcode |
Anna Bridge |
160:5571c4ff569f | 143 | * |
AnnaBridge | 171:3a7713b1edbc | 144 | * The solution to that problem is to templatize the empty class to make it |
Anna Bridge |
160:5571c4ff569f | 145 | * unique to the type it is applied to: |
Anna Bridge |
160:5571c4ff569f | 146 | * |
Anna Bridge |
160:5571c4ff569f | 147 | * @code |
AnnaBridge | 146:22da6e220af6 | 148 | * template<typename T> |
AnnaBridge | 146:22da6e220af6 | 149 | * struct A<T> { }; |
Anna Bridge |
160:5571c4ff569f | 150 | * struct B : A<B> { |
AnnaBridge | 146:22da6e220af6 | 151 | * int foo; |
AnnaBridge | 146:22da6e220af6 | 152 | * }; |
Anna Bridge |
160:5571c4ff569f | 153 | * struct C : A<C> { |
AnnaBridge | 146:22da6e220af6 | 154 | * B b; |
AnnaBridge | 146:22da6e220af6 | 155 | * }; |
Anna Bridge |
160:5571c4ff569f | 156 | * |
Anna Bridge |
160:5571c4ff569f | 157 | * // empty base optimization can be applied B and C does not refer to the same |
AnnaBridge | 146:22da6e220af6 | 158 | * // kind of A. sizeof(C) == sizeof(B) == sizeof(int). |
AnnaBridge | 146:22da6e220af6 | 159 | * @endcode |
Anna Bridge |
160:5571c4ff569f | 160 | * |
AnnaBridge | 172:65be27845400 | 161 | * @tparam T The type that should be made noncopyable. |
AnnaBridge | 171:3a7713b1edbc | 162 | * |
AnnaBridge | 171:3a7713b1edbc | 163 | * @note Compile time errors are disabled if you use the develop or release profile. |
AnnaBridge | 171:3a7713b1edbc | 164 | * To override this behavior and force compile time errors in all profiles, |
Anna Bridge |
160:5571c4ff569f | 165 | * set the configuration parameter "platform.force-non-copyable-error" to true. |
AnnaBridge | 146:22da6e220af6 | 166 | */ |
AnnaBridge | 146:22da6e220af6 | 167 | template<typename T> |
Anna Bridge |
160:5571c4ff569f | 168 | class NonCopyable { |
AnnaBridge | 171:3a7713b1edbc | 169 | #ifndef DOXYGEN_ONLY |
AnnaBridge | 146:22da6e220af6 | 170 | protected: |
Anna Bridge |
160:5571c4ff569f | 171 | /** |
AnnaBridge | 165:d1b4690b3f8b | 172 | * Disallow construction of NonCopyable objects from outside of its hierarchy. |
AnnaBridge | 146:22da6e220af6 | 173 | */ |
AnnaBridge | 146:22da6e220af6 | 174 | NonCopyable() { } |
Anna Bridge |
160:5571c4ff569f | 175 | /** |
AnnaBridge | 165:d1b4690b3f8b | 176 | * Disallow destruction of NonCopyable objects from outside of its hierarchy. |
AnnaBridge | 146:22da6e220af6 | 177 | */ |
AnnaBridge | 146:22da6e220af6 | 178 | ~NonCopyable() { } |
AnnaBridge | 146:22da6e220af6 | 179 | |
Anna Bridge |
160:5571c4ff569f | 180 | #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) |
Anna Bridge |
160:5571c4ff569f | 181 | /** |
Anna Bridge |
160:5571c4ff569f | 182 | * NonCopyable copy constructor. |
Anna Bridge |
160:5571c4ff569f | 183 | * |
AnnaBridge | 171:3a7713b1edbc | 184 | * A compile time warning is issued when this function is used, and a runtime |
AnnaBridge | 171:3a7713b1edbc | 185 | * warning is printed when the copy construction of the noncopyable happens. |
Anna Bridge |
160:5571c4ff569f | 186 | * |
Anna Bridge |
160:5571c4ff569f | 187 | * If you see this warning, your code is probably doing something unspecified. |
AnnaBridge | 171:3a7713b1edbc | 188 | * Copying of noncopyable resources can lead to resource leak and random error. |
Anna Bridge |
160:5571c4ff569f | 189 | */ |
Anna Bridge |
160:5571c4ff569f | 190 | MBED_DEPRECATED("Invalid copy construction of a NonCopyable resource.") |
AnnaBridge | 170:e95d10626187 | 191 | NonCopyable(const NonCopyable &) |
Anna Bridge |
160:5571c4ff569f | 192 | { |
Anna Bridge |
160:5571c4ff569f | 193 | debug("Invalid copy construction of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); |
Anna Bridge |
160:5571c4ff569f | 194 | } |
Anna Bridge |
160:5571c4ff569f | 195 | |
AnnaBridge | 146:22da6e220af6 | 196 | /** |
Anna Bridge |
160:5571c4ff569f | 197 | * NonCopyable copy assignment operator. |
Anna Bridge |
160:5571c4ff569f | 198 | * |
AnnaBridge | 171:3a7713b1edbc | 199 | * A compile time warning is issued when this function is used, and a runtime |
AnnaBridge | 171:3a7713b1edbc | 200 | * warning is printed when the copy construction of the noncopyable happens. |
Anna Bridge |
160:5571c4ff569f | 201 | * |
Anna Bridge |
160:5571c4ff569f | 202 | * If you see this warning, your code is probably doing something unspecified. |
AnnaBridge | 171:3a7713b1edbc | 203 | * Copying of noncopyable resources can lead to resource leak and random error. |
Anna Bridge |
160:5571c4ff569f | 204 | */ |
Anna Bridge |
160:5571c4ff569f | 205 | MBED_DEPRECATED("Invalid copy assignment of a NonCopyable resource.") |
AnnaBridge | 170:e95d10626187 | 206 | NonCopyable &operator=(const NonCopyable &) |
Anna Bridge |
160:5571c4ff569f | 207 | { |
Anna Bridge |
160:5571c4ff569f | 208 | debug("Invalid copy assignment of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); |
Anna Bridge |
160:5571c4ff569f | 209 | return *this; |
Anna Bridge |
160:5571c4ff569f | 210 | } |
Anna Bridge |
160:5571c4ff569f | 211 | |
Anna Bridge |
160:5571c4ff569f | 212 | #else |
Anna Bridge |
160:5571c4ff569f | 213 | private: |
Anna Bridge |
160:5571c4ff569f | 214 | /** |
AnnaBridge | 171:3a7713b1edbc | 215 | * Declare copy constructor as private. Any attempt to copy construct |
AnnaBridge | 146:22da6e220af6 | 216 | * a NonCopyable will fail at compile time. |
AnnaBridge | 146:22da6e220af6 | 217 | */ |
AnnaBridge | 170:e95d10626187 | 218 | NonCopyable(const NonCopyable &); |
AnnaBridge | 146:22da6e220af6 | 219 | |
AnnaBridge | 146:22da6e220af6 | 220 | /** |
AnnaBridge | 171:3a7713b1edbc | 221 | * Declare copy assignment operator as private. Any attempt to copy assign |
AnnaBridge | 146:22da6e220af6 | 222 | * a NonCopyable will fail at compile time. |
AnnaBridge | 146:22da6e220af6 | 223 | */ |
AnnaBridge | 170:e95d10626187 | 224 | NonCopyable &operator=(const NonCopyable &); |
Anna Bridge |
160:5571c4ff569f | 225 | #endif |
AnnaBridge | 172:65be27845400 | 226 | #endif |
AnnaBridge | 146:22da6e220af6 | 227 | }; |
AnnaBridge | 146:22da6e220af6 | 228 | |
AnnaBridge | 171:3a7713b1edbc | 229 | /**@}*/ |
AnnaBridge | 171:3a7713b1edbc | 230 | |
AnnaBridge | 171:3a7713b1edbc | 231 | /**@}*/ |
AnnaBridge | 171:3a7713b1edbc | 232 | |
Anna Bridge |
160:5571c4ff569f | 233 | } // namespace mbed |
AnnaBridge | 146:22da6e220af6 | 234 | |
AnnaBridge | 146:22da6e220af6 | 235 | #endif /* MBED_NONCOPYABLE_H_ */ |