Important changes to repositories hosted on mbed.com
Mbed hosted mercurial repositories are deprecated and are due to be permanently deleted in July 2026.
To keep a copy of this software download the repository Zip archive or clone locally using Mercurial.
It is also possible to export all your personal repositories from the account settings page.
Dependents: TYBLE16_simple_data_logger TYBLE16_MP3_Air
NonCopyable.h
00001 /* Copyright (c) 2017-2019 ARM Limited 00002 * SPDX-License-Identifier: Apache-2.0 00003 * 00004 * Licensed under the Apache License, Version 2.0 (the "License"); 00005 * you may not use this file except in compliance with the License. 00006 * You may obtain a copy of the License at 00007 * 00008 * http://www.apache.org/licenses/LICENSE-2.0 00009 * 00010 * Unless required by applicable law or agreed to in writing, software 00011 * distributed under the License is distributed on an "AS IS" BASIS, 00012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 00013 * See the License for the specific language governing permissions and 00014 * limitations under the License. 00015 */ 00016 00017 #ifndef MBED_NONCOPYABLE_H_ 00018 #define MBED_NONCOPYABLE_H_ 00019 00020 #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) 00021 #include "platform/mbed_toolchain.h" 00022 #include "platform/mbed_debug.h" 00023 #endif 00024 00025 namespace mbed { 00026 00027 /** \addtogroup platform-public-api */ 00028 /** @{*/ 00029 00030 /** 00031 * \defgroup platform_NonCopyable NonCopyable class 00032 * @{ 00033 */ 00034 00035 /** 00036 * Prevents generation of copy constructor and copy assignment operator in 00037 * derived classes. 00038 * 00039 * @par Usage 00040 * 00041 * To prevent generation of copy constructor and copy assignment operator, 00042 * inherit privately from the NonCopyable class. 00043 * 00044 * @code 00045 * class Resource : NonCopyable<Resource> { }; 00046 * 00047 * Resource r; 00048 * // generates compile time error: 00049 * Resource r2 = r; 00050 * @endcode 00051 * 00052 * @par Background information 00053 * 00054 * Instances of polymorphic classes are not meant to be copied. The 00055 * C++ standards generate a default copy constructor and copy assignment 00056 * function if these functions have not been defined in the class. 00057 * 00058 * Consider the following example: 00059 * 00060 * @code 00061 * // base class representing a connection 00062 * struct Connection { 00063 * Connection(); 00064 * virtual ~Connection(); 00065 * virtual void open() = 0; 00066 * } 00067 * 00068 * class SerialConnection : public Connection { 00069 * public: 00070 * SerialConnection(Serial*); 00071 * 00072 * private: 00073 * Serial* _serial; 00074 * }; 00075 * 00076 * Connection& get_connection() { 00077 * static SerialConnection serial_connection; 00078 * return serial_connection; 00079 * } 00080 * 00081 * Connection connection = get_connection(); 00082 * @endcode 00083 * 00084 * There is a subtle bug in this code, the function get_connection returns a 00085 * reference to a Connection which is captured by value instead of reference. 00086 * 00087 * When `get_connection` returns a reference to serial_connection it is copied into 00088 * the local variable connection. The vtable and others members defined in Connection 00089 * are copied, but members defined in SerialConnection are left apart. This can cause 00090 * severe crashes or bugs if the virtual functions captured use members not present 00091 * in the base declaration. 00092 * 00093 * To solve that problem, the copy constructor and assignment operator have to 00094 * be declared (but don't need to be defined) in the private section of the 00095 * Connection class: 00096 * 00097 * @code 00098 * struct Connection { 00099 * private: 00100 * Connection(const Connection&); 00101 * Connection& operator=(const Connection&); 00102 * } 00103 * @endcode 00104 * 00105 * Although manually declaring private copy constructor and assignment functions 00106 * works, it is not ideal. These declarations are usually easy to forget, 00107 * not immediately visible, and may be obscure to uninformed programmers. 00108 * 00109 * Using the NonCopyable class reduces the boilerplate required and expresses 00110 * the intent because class inheritance appears right after the class name 00111 * declaration. 00112 * 00113 * @code 00114 * struct Connection : private NonCopyable<Connection> { 00115 * // regular declarations 00116 * } 00117 * @endcode 00118 * 00119 * 00120 * @par Implementation details 00121 * 00122 * Using a template type prevents cases where the empty base optimization cannot 00123 * be applied and therefore ensures that the cost of the NonCopyable semantic 00124 * sugar is null. 00125 * 00126 * As an example, the empty base optimization is prohibited if one of the empty 00127 * base classes is also a base type of the first nonstatic data member: 00128 * 00129 * @code 00130 * struct A { }; 00131 * struct B : A { 00132 * int foo; 00133 * }; 00134 * // thanks to empty base optimization, sizeof(B) == sizeof(int) 00135 * 00136 * struct C : A { 00137 * B b; 00138 * }; 00139 * 00140 * // empty base optimization cannot be applied here because A from C and A from 00141 * // B have a different address. In that case, with the alignment 00142 * // sizeof(C) == 2* sizeof(int) 00143 * @endcode 00144 * 00145 * The solution to that problem is to templatize the empty class to make it 00146 * unique to the type it is applied to: 00147 * 00148 * @code 00149 * template<typename T> 00150 * struct A<T> { }; 00151 * struct B : A<B> { 00152 * int foo; 00153 * }; 00154 * struct C : A<C> { 00155 * B b; 00156 * }; 00157 * 00158 * // empty base optimization can be applied B and C does not refer to the same 00159 * // kind of A. sizeof(C) == sizeof(B) == sizeof(int). 00160 * @endcode 00161 * 00162 * @tparam T The type that should be made noncopyable. 00163 * 00164 * @note Compile time errors are disabled if you use the develop or release profile. 00165 * To override this behavior and force compile time errors in all profiles, 00166 * set the configuration parameter "platform.force-non-copyable-error" to true. 00167 */ 00168 template<typename T> 00169 class NonCopyable { 00170 #ifndef DOXYGEN_ONLY 00171 protected: 00172 /** 00173 * Disallow construction of NonCopyable objects from outside of its hierarchy. 00174 */ 00175 NonCopyable() = default; 00176 /** 00177 * Disallow destruction of NonCopyable objects from outside of its hierarchy. 00178 */ 00179 ~NonCopyable() = default; 00180 00181 #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0)) 00182 /** 00183 * NonCopyable copy constructor. 00184 * 00185 * A compile time warning is issued when this function is used, and a runtime 00186 * warning is printed when the copy construction of the noncopyable happens. 00187 * 00188 * If you see this warning, your code is probably doing something unspecified. 00189 * Copying of noncopyable resources can lead to resource leak and random error. 00190 */ 00191 MBED_DEPRECATED("Invalid copy construction of a NonCopyable resource.") 00192 NonCopyable(const NonCopyable &) 00193 { 00194 debug("Invalid copy construction of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); 00195 } 00196 00197 /** 00198 * NonCopyable copy assignment operator. 00199 * 00200 * A compile time warning is issued when this function is used, and a runtime 00201 * warning is printed when the copy construction of the noncopyable happens. 00202 * 00203 * If you see this warning, your code is probably doing something unspecified. 00204 * Copying of noncopyable resources can lead to resource leak and random error. 00205 */ 00206 MBED_DEPRECATED("Invalid copy assignment of a NonCopyable resource.") 00207 NonCopyable &operator=(const NonCopyable &) 00208 { 00209 debug("Invalid copy assignment of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION); 00210 return *this; 00211 } 00212 00213 #else 00214 private: 00215 /** 00216 * Declare copy constructor as private. Any attempt to copy construct 00217 * a NonCopyable will fail at compile time. 00218 */ 00219 NonCopyable(const NonCopyable &); 00220 00221 /** 00222 * Declare copy assignment operator as private. Any attempt to copy assign 00223 * a NonCopyable will fail at compile time. 00224 */ 00225 NonCopyable &operator=(const NonCopyable &); 00226 #endif 00227 #endif 00228 }; 00229 00230 /**@}*/ 00231 00232 /**@}*/ 00233 00234 } // namespace mbed 00235 00236 #endif /* MBED_NONCOPYABLE_H_ */
Generated on Tue Jul 12 2022 13:54:38 by
