BA / Mbed OS BaBoRo_test2

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mbed-os/platform/NonCopyable.h@0:02dd72d1d465, 2018-04-24 (annotated)

Committer:
borlanic
Date:
Tue Apr 24 11:45:18 2018 +0000
Revision:
0:02dd72d1d465
BaBoRo_test2 - backup 1

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borlanic 0:02dd72d1d465 1 /* Copyright (c) 2017 ARM Limited
borlanic 0:02dd72d1d465 2 *
borlanic 0:02dd72d1d465 3 * Licensed under the Apache License, Version 2.0 (the "License");
borlanic 0:02dd72d1d465 4 * you may not use this file except in compliance with the License.
borlanic 0:02dd72d1d465 5 * You may obtain a copy of the License at
borlanic 0:02dd72d1d465 6 *
borlanic 0:02dd72d1d465 7 * http://www.apache.org/licenses/LICENSE-2.0
borlanic 0:02dd72d1d465 8 *
borlanic 0:02dd72d1d465 9 * Unless required by applicable law or agreed to in writing, software
borlanic 0:02dd72d1d465 10 * distributed under the License is distributed on an "AS IS" BASIS,
borlanic 0:02dd72d1d465 11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
borlanic 0:02dd72d1d465 12 * See the License for the specific language governing permissions and
borlanic 0:02dd72d1d465 13 * limitations under the License.
borlanic 0:02dd72d1d465 14 */
borlanic 0:02dd72d1d465 15
borlanic 0:02dd72d1d465 16 #ifndef MBED_NONCOPYABLE_H_
borlanic 0:02dd72d1d465 17 #define MBED_NONCOPYABLE_H_
borlanic 0:02dd72d1d465 18
borlanic 0:02dd72d1d465 19 #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0))
borlanic 0:02dd72d1d465 20 #include "mbed_toolchain.h"
borlanic 0:02dd72d1d465 21 #include "mbed_debug.h"
borlanic 0:02dd72d1d465 22 #endif
borlanic 0:02dd72d1d465 23
borlanic 0:02dd72d1d465 24 namespace mbed {
borlanic 0:02dd72d1d465 25
borlanic 0:02dd72d1d465 26 /**
borlanic 0:02dd72d1d465 27 * Inheriting from this class autogeneration of copy construction and copy
borlanic 0:02dd72d1d465 28 * assignment operations.
borlanic 0:02dd72d1d465 29 *
borlanic 0:02dd72d1d465 30 * Classes which are not value type should inherit privately from this class
borlanic 0:02dd72d1d465 31 * to avoid generation of invalid copy constructor or copy assignment operator
borlanic 0:02dd72d1d465 32 * which can lead to unnoticeable programming errors.
borlanic 0:02dd72d1d465 33 *
borlanic 0:02dd72d1d465 34 * As an example consider the following signature:
borlanic 0:02dd72d1d465 35 *
borlanic 0:02dd72d1d465 36 * @code
borlanic 0:02dd72d1d465 37 * class Resource;
borlanic 0:02dd72d1d465 38 *
borlanic 0:02dd72d1d465 39 * class Foo {
borlanic 0:02dd72d1d465 40 * public:
borlanic 0:02dd72d1d465 41 * Foo() : _resource(new Resource()) { }
borlanic 0:02dd72d1d465 42 * ~Foo() { delete _resource; }
borlanic 0:02dd72d1d465 43 * private:
borlanic 0:02dd72d1d465 44 * Resource* _resource;
borlanic 0:02dd72d1d465 45 * }
borlanic 0:02dd72d1d465 46 *
borlanic 0:02dd72d1d465 47 * Foo get_foo();
borlanic 0:02dd72d1d465 48 *
borlanic 0:02dd72d1d465 49 * Foo foo = get_foo();
borlanic 0:02dd72d1d465 50 * @endcode
borlanic 0:02dd72d1d465 51 *
borlanic 0:02dd72d1d465 52 * There is a bug in this function, it returns a temporary value which will be
borlanic 0:02dd72d1d465 53 * byte copied into foo then destroyed. Unfortunately, internally the Foo class
borlanic 0:02dd72d1d465 54 * manage a pointer to a Resource object. This pointer will be released when the
borlanic 0:02dd72d1d465 55 * temporary is destroyed and foo will manage a pointer to an already released
borlanic 0:02dd72d1d465 56 * Resource.
borlanic 0:02dd72d1d465 57 *
borlanic 0:02dd72d1d465 58 * Two issues has to be fixed in the example above:
borlanic 0:02dd72d1d465 59 * - Function signature has to be changed to reflect the fact that Foo
borlanic 0:02dd72d1d465 60 * instances cannot be copied. In that case accessor should return a
borlanic 0:02dd72d1d465 61 * reference to give access to objects already existing and managed.
borlanic 0:02dd72d1d465 62 * Generator on the other hand should return a pointer to the created object.
borlanic 0:02dd72d1d465 63 *
borlanic 0:02dd72d1d465 64 * @code
borlanic 0:02dd72d1d465 65 * // return a reference to an already managed Foo instance
borlanic 0:02dd72d1d465 66 * Foo& get_foo();
borlanic 0:02dd72d1d465 67 * Foo& foo = get_foo();
borlanic 0:02dd72d1d465 68 *
borlanic 0:02dd72d1d465 69 * // create a new Foo instance
borlanic 0:02dd72d1d465 70 * Foo* make_foo();
borlanic 0:02dd72d1d465 71 * Foo* m = make_foo();
borlanic 0:02dd72d1d465 72 * @endcode
borlanic 0:02dd72d1d465 73 *
borlanic 0:02dd72d1d465 74 * - Copy constructor and copy assignment operator has to be made private
borlanic 0:02dd72d1d465 75 * in the Foo class. It prevents unwanted copy of Foo objects. This can be
borlanic 0:02dd72d1d465 76 * done by declaring copy constructor and copy assignment in the private
borlanic 0:02dd72d1d465 77 * section of the Foo class.
borlanic 0:02dd72d1d465 78 *
borlanic 0:02dd72d1d465 79 * @code
borlanic 0:02dd72d1d465 80 * class Foo {
borlanic 0:02dd72d1d465 81 * public:
borlanic 0:02dd72d1d465 82 * Foo() : _resource(new Resource()) { }
borlanic 0:02dd72d1d465 83 * ~Foo() { delete _resource; }
borlanic 0:02dd72d1d465 84 * private:
borlanic 0:02dd72d1d465 85 * // disallow copy operations
borlanic 0:02dd72d1d465 86 * Foo(const Foo&);
borlanic 0:02dd72d1d465 87 * Foo& operator=(const Foo&);
borlanic 0:02dd72d1d465 88 * // data members
borlanic 0:02dd72d1d465 89 * Resource* _resource;
borlanic 0:02dd72d1d465 90 * }
borlanic 0:02dd72d1d465 91 * @endcode
borlanic 0:02dd72d1d465 92 *
borlanic 0:02dd72d1d465 93 * Another solution is to inherit privately from the NonCopyable class.
borlanic 0:02dd72d1d465 94 * It reduces the boiler plate needed to avoid copy operations but more
borlanic 0:02dd72d1d465 95 * importantly it clarifies the programmer intent and the object semantic.
borlanic 0:02dd72d1d465 96 *
borlanic 0:02dd72d1d465 97 * class Foo : private NonCopyable<Foo> {
borlanic 0:02dd72d1d465 98 * public:
borlanic 0:02dd72d1d465 99 * Foo() : _resource(new Resource()) { }
borlanic 0:02dd72d1d465 100 * ~Foo() { delete _resource; }
borlanic 0:02dd72d1d465 101 * private:
borlanic 0:02dd72d1d465 102 * Resource* _resource;
borlanic 0:02dd72d1d465 103 * }
borlanic 0:02dd72d1d465 104 *
borlanic 0:02dd72d1d465 105 * @tparam T The type that should be made non copyable. It prevent cases where
borlanic 0:02dd72d1d465 106 * the empty base optimization cannot be applied and therefore ensure that the
borlanic 0:02dd72d1d465 107 * cost of this semantic sugar is null.
borlanic 0:02dd72d1d465 108 *
borlanic 0:02dd72d1d465 109 * As an example, the empty base optimization is prohibited if one of the empty
borlanic 0:02dd72d1d465 110 * base class is also a base type of the first non static data member:
borlanic 0:02dd72d1d465 111 *
borlanic 0:02dd72d1d465 112 * @code
borlanic 0:02dd72d1d465 113 * struct A { };
borlanic 0:02dd72d1d465 114 * struct B : A {
borlanic 0:02dd72d1d465 115 * int foo;
borlanic 0:02dd72d1d465 116 * };
borlanic 0:02dd72d1d465 117 * // thanks to empty base optimization, sizeof(B) == sizeof(int)
borlanic 0:02dd72d1d465 118 *
borlanic 0:02dd72d1d465 119 * struct C : A {
borlanic 0:02dd72d1d465 120 * B b;
borlanic 0:02dd72d1d465 121 * };
borlanic 0:02dd72d1d465 122 *
borlanic 0:02dd72d1d465 123 * // empty base optimization cannot be applied here because A from C and A from
borlanic 0:02dd72d1d465 124 * // B shall have a different address. In that case, with the alignment
borlanic 0:02dd72d1d465 125 * // sizeof(C) == 2* sizeof(int)
borlanic 0:02dd72d1d465 126 * @endcode
borlanic 0:02dd72d1d465 127 *
borlanic 0:02dd72d1d465 128 * The solution to that problem is to templatize the empty class to makes it
borlanic 0:02dd72d1d465 129 * unique to the type it is applied to:
borlanic 0:02dd72d1d465 130 *
borlanic 0:02dd72d1d465 131 * @code
borlanic 0:02dd72d1d465 132 * template<typename T>
borlanic 0:02dd72d1d465 133 * struct A<T> { };
borlanic 0:02dd72d1d465 134 * struct B : A<B> {
borlanic 0:02dd72d1d465 135 * int foo;
borlanic 0:02dd72d1d465 136 * };
borlanic 0:02dd72d1d465 137 * struct C : A<C> {
borlanic 0:02dd72d1d465 138 * B b;
borlanic 0:02dd72d1d465 139 * };
borlanic 0:02dd72d1d465 140 *
borlanic 0:02dd72d1d465 141 * // empty base optimization can be applied B and C does not refer to the same
borlanic 0:02dd72d1d465 142 * // kind of A. sizeof(C) == sizeof(B) == sizeof(int).
borlanic 0:02dd72d1d465 143 * @endcode
borlanic 0:02dd72d1d465 144 *
borlanic 0:02dd72d1d465 145 * @note Compile time errors are disabled if the develop or the release profile
borlanic 0:02dd72d1d465 146 * is used. To override this behavior and force compile time errors in all profile
borlanic 0:02dd72d1d465 147 * set the configuration parameter "platform.force-non-copyable-error" to true.
borlanic 0:02dd72d1d465 148 */
borlanic 0:02dd72d1d465 149 template<typename T>
borlanic 0:02dd72d1d465 150 class NonCopyable {
borlanic 0:02dd72d1d465 151 protected:
borlanic 0:02dd72d1d465 152 /**
borlanic 0:02dd72d1d465 153 * Disallow construction of NonCopyable objects from outside of its hierarchy.
borlanic 0:02dd72d1d465 154 */
borlanic 0:02dd72d1d465 155 NonCopyable() { }
borlanic 0:02dd72d1d465 156 /**
borlanic 0:02dd72d1d465 157 * Disallow destruction of NonCopyable objects from outside of its hierarchy.
borlanic 0:02dd72d1d465 158 */
borlanic 0:02dd72d1d465 159 ~NonCopyable() { }
borlanic 0:02dd72d1d465 160
borlanic 0:02dd72d1d465 161 #if (!defined(MBED_DEBUG) && (MBED_CONF_PLATFORM_FORCE_NON_COPYABLE_ERROR == 0))
borlanic 0:02dd72d1d465 162 /**
borlanic 0:02dd72d1d465 163 * NonCopyable copy constructor.
borlanic 0:02dd72d1d465 164 *
borlanic 0:02dd72d1d465 165 * A compile time warning is issued when this function is used and a runtime
borlanic 0:02dd72d1d465 166 * warning is printed when the copy construction of the non copyable happens.
borlanic 0:02dd72d1d465 167 *
borlanic 0:02dd72d1d465 168 * If you see this warning, your code is probably doing something unspecified.
borlanic 0:02dd72d1d465 169 * Copy of non copyable resources can lead to resource leak and random error.
borlanic 0:02dd72d1d465 170 */
borlanic 0:02dd72d1d465 171 MBED_DEPRECATED("Invalid copy construction of a NonCopyable resource.")
borlanic 0:02dd72d1d465 172 NonCopyable(const NonCopyable&)
borlanic 0:02dd72d1d465 173 {
borlanic 0:02dd72d1d465 174 debug("Invalid copy construction of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION);
borlanic 0:02dd72d1d465 175 }
borlanic 0:02dd72d1d465 176
borlanic 0:02dd72d1d465 177 /**
borlanic 0:02dd72d1d465 178 * NonCopyable copy assignment operator.
borlanic 0:02dd72d1d465 179 *
borlanic 0:02dd72d1d465 180 * A compile time warning is issued when this function is used and a runtime
borlanic 0:02dd72d1d465 181 * warning is printed when the copy construction of the non copyable happens.
borlanic 0:02dd72d1d465 182 *
borlanic 0:02dd72d1d465 183 * If you see this warning, your code is probably doing something unspecified.
borlanic 0:02dd72d1d465 184 * Copy of non copyable resources can lead to resource leak and random error.
borlanic 0:02dd72d1d465 185 */
borlanic 0:02dd72d1d465 186 MBED_DEPRECATED("Invalid copy assignment of a NonCopyable resource.")
borlanic 0:02dd72d1d465 187 NonCopyable& operator=(const NonCopyable&)
borlanic 0:02dd72d1d465 188 {
borlanic 0:02dd72d1d465 189 debug("Invalid copy assignment of a NonCopyable resource: %s\r\n", MBED_PRETTY_FUNCTION);
borlanic 0:02dd72d1d465 190 return *this;
borlanic 0:02dd72d1d465 191 }
borlanic 0:02dd72d1d465 192
borlanic 0:02dd72d1d465 193 #else
borlanic 0:02dd72d1d465 194 private:
borlanic 0:02dd72d1d465 195 /**
borlanic 0:02dd72d1d465 196 * Declare copy constructor as private, any attempt to copy construct
borlanic 0:02dd72d1d465 197 * a NonCopyable will fail at compile time.
borlanic 0:02dd72d1d465 198 */
borlanic 0:02dd72d1d465 199 NonCopyable(const NonCopyable&);
borlanic 0:02dd72d1d465 200
borlanic 0:02dd72d1d465 201 /**
borlanic 0:02dd72d1d465 202 * Declare copy assignment operator as private, any attempt to copy assign
borlanic 0:02dd72d1d465 203 * a NonCopyable will fail at compile time.
borlanic 0:02dd72d1d465 204 */
borlanic 0:02dd72d1d465 205 NonCopyable& operator=(const NonCopyable&);
borlanic 0:02dd72d1d465 206 #endif
borlanic 0:02dd72d1d465 207 };
borlanic 0:02dd72d1d465 208
borlanic 0:02dd72d1d465 209 } // namespace mbed
borlanic 0:02dd72d1d465 210
borlanic 0:02dd72d1d465 211 #endif /* MBED_NONCOPYABLE_H_ */