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platform/NonCopyable.h@2:7aab896b1a3b, 2019-03-13 (annotated)
- Committer:
- kevman
- Date:
- Wed Mar 13 11:03:24 2019 +0000
- Revision:
- 2:7aab896b1a3b
- Parent:
- 0:38ceb79fef03
2019-03-13
Who changed what in which revision?
User | Revision | Line number | New contents of line |
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kevman | 0:38ceb79fef03 | 1 | /* Copyright (c) 2017 ARM Limited |
kevman | 0:38ceb79fef03 | 2 | * |
kevman | 0:38ceb79fef03 | 3 | * Licensed under the Apache License, Version 2.0 (the "License"); |
kevman | 0:38ceb79fef03 | 4 | * you may not use this file except in compliance with the License. |
kevman | 0:38ceb79fef03 | 5 | * You may obtain a copy of the License at |
kevman | 0:38ceb79fef03 | 6 | * |
kevman | 0:38ceb79fef03 | 7 | * http://www.apache.org/licenses/LICENSE-2.0 |
kevman | 0:38ceb79fef03 | 8 | * |
kevman | 0:38ceb79fef03 | 9 | * Unless required by applicable law or agreed to in writing, software |
kevman | 0:38ceb79fef03 | 10 | * distributed under the License is distributed on an "AS IS" BASIS, |
kevman | 0:38ceb79fef03 | 11 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
kevman | 0:38ceb79fef03 | 12 | * See the License for the specific language governing permissions and |
kevman | 0:38ceb79fef03 | 13 | * limitations under the License. |
kevman | 0:38ceb79fef03 | 14 | */ |
kevman | 0:38ceb79fef03 | 15 | |
kevman | 0:38ceb79fef03 | 16 | #ifndef MBED_NONCOPYABLE_H_ |
kevman | 0:38ceb79fef03 | 17 | #define MBED_NONCOPYABLE_H_ |
kevman | 0:38ceb79fef03 | 18 | |
kevman | 0:38ceb79fef03 | 19 | #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) |
kevman | 0:38ceb79fef03 | 20 | #include "mbed_toolchain.h" |
kevman | 0:38ceb79fef03 | 21 | #include "mbed_debug.h" |
kevman | 0:38ceb79fef03 | 22 | #endif |
kevman | 0:38ceb79fef03 | 23 | |
kevman | 0:38ceb79fef03 | 24 | namespace mbed { |
kevman | 0:38ceb79fef03 | 25 | |
kevman | 0:38ceb79fef03 | 26 | /** \addtogroup platform */ |
kevman | 0:38ceb79fef03 | 27 | /** @{*/ |
kevman | 0:38ceb79fef03 | 28 | /** |
kevman | 0:38ceb79fef03 | 29 | * \defgroup platform_NonCopyable NonCopyable class |
kevman | 0:38ceb79fef03 | 30 | * @{ |
kevman | 0:38ceb79fef03 | 31 | */ |
kevman | 0:38ceb79fef03 | 32 | |
kevman | 0:38ceb79fef03 | 33 | /** |
kevman | 0:38ceb79fef03 | 34 | * Prevents generation of copy constructor and copy assignment operator in |
kevman | 0:38ceb79fef03 | 35 | * derived classes. |
kevman | 0:38ceb79fef03 | 36 | * |
kevman | 0:38ceb79fef03 | 37 | * @par Usage |
kevman | 0:38ceb79fef03 | 38 | * |
kevman | 0:38ceb79fef03 | 39 | * To prevent generation of copy constructor and copy assignment operator, |
kevman | 0:38ceb79fef03 | 40 | * inherit privately from the NonCopyable class. |
kevman | 0:38ceb79fef03 | 41 | * |
kevman | 0:38ceb79fef03 | 42 | * @code |
kevman | 0:38ceb79fef03 | 43 | * class Resource : NonCopyable<Resource> { }; |
kevman | 0:38ceb79fef03 | 44 | * |
kevman | 0:38ceb79fef03 | 45 | * Resource r; |
kevman | 0:38ceb79fef03 | 46 | * // generates compile time error: |
kevman | 0:38ceb79fef03 | 47 | * Resource r2 = r; |
kevman | 0:38ceb79fef03 | 48 | * @endcode |
kevman | 0:38ceb79fef03 | 49 | * |
kevman | 0:38ceb79fef03 | 50 | * @par Background information |
kevman | 0:38ceb79fef03 | 51 | * |
kevman | 0:38ceb79fef03 | 52 | * Instances of polymorphic classes are not meant to be copied. The |
kevman | 0:38ceb79fef03 | 53 | * C++ standards generate a default copy constructor and copy assignment |
kevman | 0:38ceb79fef03 | 54 | * function if these functions have not been defined in the class. |
kevman | 0:38ceb79fef03 | 55 | * |
kevman | 0:38ceb79fef03 | 56 | * Consider the following example: |
kevman | 0:38ceb79fef03 | 57 | * |
kevman | 0:38ceb79fef03 | 58 | * @code |
kevman | 0:38ceb79fef03 | 59 | * // base class representing a connection |
kevman | 0:38ceb79fef03 | 60 | * struct Connection { |
kevman | 0:38ceb79fef03 | 61 | * Connection(); |
kevman | 0:38ceb79fef03 | 62 | * virtual ~Connection(); |
kevman | 0:38ceb79fef03 | 63 | * virtual void open() = 0; |
kevman | 0:38ceb79fef03 | 64 | * } |
kevman | 0:38ceb79fef03 | 65 | * |
kevman | 0:38ceb79fef03 | 66 | * class SerialConnection : public Connection { |
kevman | 0:38ceb79fef03 | 67 | * public: |
kevman | 0:38ceb79fef03 | 68 | * SerialConnection(Serial*); |
kevman | 0:38ceb79fef03 | 69 | * |
kevman | 0:38ceb79fef03 | 70 | * private: |
kevman | 0:38ceb79fef03 | 71 | * Serial* _serial; |
kevman | 0:38ceb79fef03 | 72 | * }; |
kevman | 0:38ceb79fef03 | 73 | * |
kevman | 0:38ceb79fef03 | 74 | * Connection& get_connection() { |
kevman | 0:38ceb79fef03 | 75 | * static SerialConnection serial_connection; |
kevman | 0:38ceb79fef03 | 76 | * return serial_connection; |
kevman | 0:38ceb79fef03 | 77 | * } |
kevman | 0:38ceb79fef03 | 78 | * |
kevman | 0:38ceb79fef03 | 79 | * Connection connection = get_connection(); |
kevman | 0:38ceb79fef03 | 80 | * @endcode |
kevman | 0:38ceb79fef03 | 81 | * |
kevman | 0:38ceb79fef03 | 82 | * There is a subtle bug in this code, the function get_connection returns a |
kevman | 0:38ceb79fef03 | 83 | * reference to a Connection which is captured by value instead of reference. |
kevman | 0:38ceb79fef03 | 84 | * |
kevman | 0:38ceb79fef03 | 85 | * When `get_connection` returns a reference to serial_connection it is copied into |
kevman | 0:38ceb79fef03 | 86 | * the local variable connection. The vtable and others members defined in Connection |
kevman | 0:38ceb79fef03 | 87 | * are copied, but members defined in SerialConnection are left apart. This can cause |
kevman | 0:38ceb79fef03 | 88 | * severe crashes or bugs if the virtual functions captured use members not present |
kevman | 0:38ceb79fef03 | 89 | * in the base declaration. |
kevman | 0:38ceb79fef03 | 90 | * |
kevman | 0:38ceb79fef03 | 91 | * To solve that problem, the copy constructor and assignment operator have to |
kevman | 0:38ceb79fef03 | 92 | * be declared (but don't need to be defined) in the private section of the |
kevman | 0:38ceb79fef03 | 93 | * Connection class: |
kevman | 0:38ceb79fef03 | 94 | * |
kevman | 0:38ceb79fef03 | 95 | * @code |
kevman | 0:38ceb79fef03 | 96 | * struct Connection { |
kevman | 0:38ceb79fef03 | 97 | * private: |
kevman | 0:38ceb79fef03 | 98 | * Connection(const Connection&); |
kevman | 0:38ceb79fef03 | 99 | * Connection& operator=(const Connection&); |
kevman | 0:38ceb79fef03 | 100 | * } |
kevman | 0:38ceb79fef03 | 101 | * @endcode |
kevman | 0:38ceb79fef03 | 102 | * |
kevman | 0:38ceb79fef03 | 103 | * Although manually declaring private copy constructor and assignment functions |
kevman | 0:38ceb79fef03 | 104 | * works, it is not ideal. These declarations are usually easy to forget, |
kevman | 0:38ceb79fef03 | 105 | * not immediately visible, and may be obscure to uninformed programmers. |
kevman | 0:38ceb79fef03 | 106 | * |
kevman | 0:38ceb79fef03 | 107 | * Using the NonCopyable class reduces the boilerplate required and expresses |
kevman | 0:38ceb79fef03 | 108 | * the intent because class inheritance appears right after the class name |
kevman | 0:38ceb79fef03 | 109 | * declaration. |
kevman | 0:38ceb79fef03 | 110 | * |
kevman | 0:38ceb79fef03 | 111 | * @code |
kevman | 0:38ceb79fef03 | 112 | * struct Connection : private NonCopyable<Connection> { |
kevman | 0:38ceb79fef03 | 113 | * // regular declarations |
kevman | 0:38ceb79fef03 | 114 | * } |
kevman | 0:38ceb79fef03 | 115 | * @endcode |
kevman | 0:38ceb79fef03 | 116 | * |
kevman | 0:38ceb79fef03 | 117 | * |
kevman | 0:38ceb79fef03 | 118 | * @par Implementation details |
kevman | 0:38ceb79fef03 | 119 | * |
kevman | 0:38ceb79fef03 | 120 | * Using a template type prevents cases where the empty base optimization cannot |
kevman | 0:38ceb79fef03 | 121 | * be applied and therefore ensures that the cost of the NonCopyable semantic |
kevman | 0:38ceb79fef03 | 122 | * sugar is null. |
kevman | 0:38ceb79fef03 | 123 | * |
kevman | 0:38ceb79fef03 | 124 | * As an example, the empty base optimization is prohibited if one of the empty |
kevman | 0:38ceb79fef03 | 125 | * base classes is also a base type of the first nonstatic data member: |
kevman | 0:38ceb79fef03 | 126 | * |
kevman | 0:38ceb79fef03 | 127 | * @code |
kevman | 0:38ceb79fef03 | 128 | * struct A { }; |
kevman | 0:38ceb79fef03 | 129 | * struct B : A { |
kevman | 0:38ceb79fef03 | 130 | * int foo; |
kevman | 0:38ceb79fef03 | 131 | * }; |
kevman | 0:38ceb79fef03 | 132 | * // thanks to empty base optimization, sizeof(B) == sizeof(int) |
kevman | 0:38ceb79fef03 | 133 | * |
kevman | 0:38ceb79fef03 | 134 | * struct C : A { |
kevman | 0:38ceb79fef03 | 135 | * B b; |
kevman | 0:38ceb79fef03 | 136 | * }; |
kevman | 0:38ceb79fef03 | 137 | * |
kevman | 0:38ceb79fef03 | 138 | * // empty base optimization cannot be applied here because A from C and A from |
kevman | 0:38ceb79fef03 | 139 | * // B have a different address. In that case, with the alignment |
kevman | 0:38ceb79fef03 | 140 | * // sizeof(C) == 2* sizeof(int) |
kevman | 0:38ceb79fef03 | 141 | * @endcode |
kevman | 0:38ceb79fef03 | 142 | * |
kevman | 0:38ceb79fef03 | 143 | * The solution to that problem is to templatize the empty class to make it |
kevman | 0:38ceb79fef03 | 144 | * unique to the type it is applied to: |
kevman | 0:38ceb79fef03 | 145 | * |
kevman | 0:38ceb79fef03 | 146 | * @code |
kevman | 0:38ceb79fef03 | 147 | * template<typename T> |
kevman | 0:38ceb79fef03 | 148 | * struct A<T> { }; |
kevman | 0:38ceb79fef03 | 149 | * struct B : A<B> { |
kevman | 0:38ceb79fef03 | 150 | * int foo; |
kevman | 0:38ceb79fef03 | 151 | * }; |
kevman | 0:38ceb79fef03 | 152 | * struct C : A<C> { |
kevman | 0:38ceb79fef03 | 153 | * B b; |
kevman | 0:38ceb79fef03 | 154 | * }; |
kevman | 0:38ceb79fef03 | 155 | * |
kevman | 0:38ceb79fef03 | 156 | * // empty base optimization can be applied B and C does not refer to the same |
kevman | 0:38ceb79fef03 | 157 | * // kind of A. sizeof(C) == sizeof(B) == sizeof(int). |
kevman | 0:38ceb79fef03 | 158 | * @endcode |
kevman | 0:38ceb79fef03 | 159 | * |
kevman | 0:38ceb79fef03 | 160 | * @tparam T The type that should be made noncopyable. |
kevman | 0:38ceb79fef03 | 161 | * |
kevman | 0:38ceb79fef03 | 162 | * @note Compile time errors are disabled if you use the develop or release profile. |
kevman | 0:38ceb79fef03 | 163 | * To override this behavior and force compile time errors in all profiles, |
kevman | 0:38ceb79fef03 | 164 | * set the configuration parameter "platform.force-non-copyable-error" to true. |
kevman | 0:38ceb79fef03 | 165 | */ |
kevman | 0:38ceb79fef03 | 166 | template<typename T> |
kevman | 0:38ceb79fef03 | 167 | class NonCopyable { |
kevman | 0:38ceb79fef03 | 168 | #ifndef DOXYGEN_ONLY |
kevman | 0:38ceb79fef03 | 169 | protected: |
kevman | 0:38ceb79fef03 | 170 | /** |
kevman | 0:38ceb79fef03 | 171 | * Disallow construction of NonCopyable objects from outside of its hierarchy. |
kevman | 0:38ceb79fef03 | 172 | */ |
kevman | 0:38ceb79fef03 | 173 | NonCopyable() { } |
kevman | 0:38ceb79fef03 | 174 | /** |
kevman | 0:38ceb79fef03 | 175 | * Disallow destruction of NonCopyable objects from outside of its hierarchy. |
kevman | 0:38ceb79fef03 | 176 | */ |
kevman | 0:38ceb79fef03 | 177 | ~NonCopyable() { } |
kevman | 0:38ceb79fef03 | 178 | |
kevman | 0:38ceb79fef03 | 179 | #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) |
kevman | 0:38ceb79fef03 | 180 | /** |
kevman | 0:38ceb79fef03 | 181 | * NonCopyable copy constructor. |
kevman | 0:38ceb79fef03 | 182 | * |
kevman | 0:38ceb79fef03 | 183 | * A compile time warning is issued when this function is used, and a runtime |
kevman | 0:38ceb79fef03 | 184 | * warning is printed when the copy construction of the noncopyable happens. |
kevman | 0:38ceb79fef03 | 185 | * |
kevman | 0:38ceb79fef03 | 186 | * If you see this warning, your code is probably doing something unspecified. |
kevman | 0:38ceb79fef03 | 187 | * Copying of noncopyable resources can lead to resource leak and random error. |
kevman | 0:38ceb79fef03 | 188 | */ |
kevman | 0:38ceb79fef03 | 189 | MBED_DEPRECATED("Invalid copy construction of a NonCopyable resource.") |
kevman | 0:38ceb79fef03 | 190 | NonCopyable(const NonCopyable &) |
kevman | 0:38ceb79fef03 | 191 | { |
kevman | 0:38ceb79fef03 | 192 | debug("Invalid copy construction of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); |
kevman | 0:38ceb79fef03 | 193 | } |
kevman | 0:38ceb79fef03 | 194 | |
kevman | 0:38ceb79fef03 | 195 | /** |
kevman | 0:38ceb79fef03 | 196 | * NonCopyable copy assignment operator. |
kevman | 0:38ceb79fef03 | 197 | * |
kevman | 0:38ceb79fef03 | 198 | * A compile time warning is issued when this function is used, and a runtime |
kevman | 0:38ceb79fef03 | 199 | * warning is printed when the copy construction of the noncopyable happens. |
kevman | 0:38ceb79fef03 | 200 | * |
kevman | 0:38ceb79fef03 | 201 | * If you see this warning, your code is probably doing something unspecified. |
kevman | 0:38ceb79fef03 | 202 | * Copying of noncopyable resources can lead to resource leak and random error. |
kevman | 0:38ceb79fef03 | 203 | */ |
kevman | 0:38ceb79fef03 | 204 | MBED_DEPRECATED("Invalid copy assignment of a NonCopyable resource.") |
kevman | 0:38ceb79fef03 | 205 | NonCopyable &operator=(const NonCopyable &) |
kevman | 0:38ceb79fef03 | 206 | { |
kevman | 0:38ceb79fef03 | 207 | debug("Invalid copy assignment of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); |
kevman | 0:38ceb79fef03 | 208 | return *this; |
kevman | 0:38ceb79fef03 | 209 | } |
kevman | 0:38ceb79fef03 | 210 | |
kevman | 0:38ceb79fef03 | 211 | #else |
kevman | 0:38ceb79fef03 | 212 | private: |
kevman | 0:38ceb79fef03 | 213 | /** |
kevman | 0:38ceb79fef03 | 214 | * Declare copy constructor as private. Any attempt to copy construct |
kevman | 0:38ceb79fef03 | 215 | * a NonCopyable will fail at compile time. |
kevman | 0:38ceb79fef03 | 216 | */ |
kevman | 0:38ceb79fef03 | 217 | NonCopyable(const NonCopyable &); |
kevman | 0:38ceb79fef03 | 218 | |
kevman | 0:38ceb79fef03 | 219 | /** |
kevman | 0:38ceb79fef03 | 220 | * Declare copy assignment operator as private. Any attempt to copy assign |
kevman | 0:38ceb79fef03 | 221 | * a NonCopyable will fail at compile time. |
kevman | 0:38ceb79fef03 | 222 | */ |
kevman | 0:38ceb79fef03 | 223 | NonCopyable &operator=(const NonCopyable &); |
kevman | 0:38ceb79fef03 | 224 | #endif |
kevman | 0:38ceb79fef03 | 225 | #endif |
kevman | 0:38ceb79fef03 | 226 | }; |
kevman | 0:38ceb79fef03 | 227 | |
kevman | 0:38ceb79fef03 | 228 | /**@}*/ |
kevman | 0:38ceb79fef03 | 229 | |
kevman | 0:38ceb79fef03 | 230 | /**@}*/ |
kevman | 0:38ceb79fef03 | 231 | |
kevman | 0:38ceb79fef03 | 232 | } // namespace mbed |
kevman | 0:38ceb79fef03 | 233 | |
kevman | 0:38ceb79fef03 | 234 | #endif /* MBED_NONCOPYABLE_H_ */ |