Simon Cooksey / mbed-os

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features/FEATURE_BLE/ble/SafeBool.h@0:fb7af294d5d9, 2016-11-17 (annotated)

Committer:
Simon Cooksey
Date:
Thu Nov 17 16:43:53 2016 +0000
Revision:
0:fb7af294d5d9
Initial commit

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Simon Cooksey 0:fb7af294d5d9 1 /* mbed Microcontroller Library
Simon Cooksey 0:fb7af294d5d9 2 * Copyright (c) 2006-2013 ARM Limited
Simon Cooksey 0:fb7af294d5d9 3 *
Simon Cooksey 0:fb7af294d5d9 4 * Licensed under the Apache License, Version 2.0 (the "License");
Simon Cooksey 0:fb7af294d5d9 5 * you may not use this file except in compliance with the License.
Simon Cooksey 0:fb7af294d5d9 6 * You may obtain a copy of the License at
Simon Cooksey 0:fb7af294d5d9 7 *
Simon Cooksey 0:fb7af294d5d9 8 * http://www.apache.org/licenses/LICENSE-2.0
Simon Cooksey 0:fb7af294d5d9 9 *
Simon Cooksey 0:fb7af294d5d9 10 * Unless required by applicable law or agreed to in writing, software
Simon Cooksey 0:fb7af294d5d9 11 * distributed under the License is distributed on an "AS IS" BASIS,
Simon Cooksey 0:fb7af294d5d9 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
Simon Cooksey 0:fb7af294d5d9 13 * See the License for the specific language governing permissions and
Simon Cooksey 0:fb7af294d5d9 14 * limitations under the License.
Simon Cooksey 0:fb7af294d5d9 15 */
Simon Cooksey 0:fb7af294d5d9 16
Simon Cooksey 0:fb7af294d5d9 17 #ifndef BLE_API_SAFE_BOOL_H_
Simon Cooksey 0:fb7af294d5d9 18 #define BLE_API_SAFE_BOOL_H_
Simon Cooksey 0:fb7af294d5d9 19
Simon Cooksey 0:fb7af294d5d9 20 /* Safe bool idiom, see : http://www.artima.com/cppsource/safebool.html */
Simon Cooksey 0:fb7af294d5d9 21
Simon Cooksey 0:fb7af294d5d9 22 namespace SafeBool_ {
Simon Cooksey 0:fb7af294d5d9 23 /**
Simon Cooksey 0:fb7af294d5d9 24 * @brief Base class for all intances of SafeBool.
Simon Cooksey 0:fb7af294d5d9 25 * This base class reduces instantiation of trueTag function.
Simon Cooksey 0:fb7af294d5d9 26 */
Simon Cooksey 0:fb7af294d5d9 27 class base {
Simon Cooksey 0:fb7af294d5d9 28 template<typename>
Simon Cooksey 0:fb7af294d5d9 29 friend class SafeBool;
Simon Cooksey 0:fb7af294d5d9 30
Simon Cooksey 0:fb7af294d5d9 31 protected:
Simon Cooksey 0:fb7af294d5d9 32 /**
Simon Cooksey 0:fb7af294d5d9 33 * The bool type is a pointer to method which can be used in boolean context.
Simon Cooksey 0:fb7af294d5d9 34 */
Simon Cooksey 0:fb7af294d5d9 35 typedef void (base::*BoolType_t)() const;
Simon Cooksey 0:fb7af294d5d9 36
Simon Cooksey 0:fb7af294d5d9 37 /**
Simon Cooksey 0:fb7af294d5d9 38 * Non implemented call, use to disallow conversion between unrelated types.
Simon Cooksey 0:fb7af294d5d9 39 */
Simon Cooksey 0:fb7af294d5d9 40 void invalidTag() const;
Simon Cooksey 0:fb7af294d5d9 41
Simon Cooksey 0:fb7af294d5d9 42 /**
Simon Cooksey 0:fb7af294d5d9 43 * Member function which indicate true value.
Simon Cooksey 0:fb7af294d5d9 44 */
Simon Cooksey 0:fb7af294d5d9 45 void trueTag() const {}
Simon Cooksey 0:fb7af294d5d9 46 };
Simon Cooksey 0:fb7af294d5d9 47
Simon Cooksey 0:fb7af294d5d9 48
Simon Cooksey 0:fb7af294d5d9 49 }
Simon Cooksey 0:fb7af294d5d9 50
Simon Cooksey 0:fb7af294d5d9 51 /**
Simon Cooksey 0:fb7af294d5d9 52 * @brief template class SafeBool use CRTP to made boolean conversion easy and correct.
Simon Cooksey 0:fb7af294d5d9 53 * Derived class should implement the function bool toBool() const to make this work. Inheritance
Simon Cooksey 0:fb7af294d5d9 54 * should be public.
Simon Cooksey 0:fb7af294d5d9 55 *
Simon Cooksey 0:fb7af294d5d9 56 * @tparam T Type of the derived class
Simon Cooksey 0:fb7af294d5d9 57 *
Simon Cooksey 0:fb7af294d5d9 58 * @code
Simon Cooksey 0:fb7af294d5d9 59 *
Simon Cooksey 0:fb7af294d5d9 60 * class A : public SafeBool<A> {
Simon Cooksey 0:fb7af294d5d9 61 * public:
Simon Cooksey 0:fb7af294d5d9 62 *
Simon Cooksey 0:fb7af294d5d9 63 * // boolean conversion
Simon Cooksey 0:fb7af294d5d9 64 * bool toBool() {
Simon Cooksey 0:fb7af294d5d9 65 *
Simon Cooksey 0:fb7af294d5d9 66 * }
Simon Cooksey 0:fb7af294d5d9 67 * };
Simon Cooksey 0:fb7af294d5d9 68 *
Simon Cooksey 0:fb7af294d5d9 69 * class B : public SafeBool<B> {
Simon Cooksey 0:fb7af294d5d9 70 * public:
Simon Cooksey 0:fb7af294d5d9 71 *
Simon Cooksey 0:fb7af294d5d9 72 * // boolean conversion
Simon Cooksey 0:fb7af294d5d9 73 * bool toBool() const {
Simon Cooksey 0:fb7af294d5d9 74 *
Simon Cooksey 0:fb7af294d5d9 75 * }
Simon Cooksey 0:fb7af294d5d9 76 * };
Simon Cooksey 0:fb7af294d5d9 77 *
Simon Cooksey 0:fb7af294d5d9 78 * A a;
Simon Cooksey 0:fb7af294d5d9 79 * B b;
Simon Cooksey 0:fb7af294d5d9 80 *
Simon Cooksey 0:fb7af294d5d9 81 * // will compile
Simon Cooksey 0:fb7af294d5d9 82 * if(a) {
Simon Cooksey 0:fb7af294d5d9 83 *
Simon Cooksey 0:fb7af294d5d9 84 * }
Simon Cooksey 0:fb7af294d5d9 85 *
Simon Cooksey 0:fb7af294d5d9 86 * // compilation error
Simon Cooksey 0:fb7af294d5d9 87 * if(a == b) {
Simon Cooksey 0:fb7af294d5d9 88 *
Simon Cooksey 0:fb7af294d5d9 89 * }
Simon Cooksey 0:fb7af294d5d9 90 *
Simon Cooksey 0:fb7af294d5d9 91 *
Simon Cooksey 0:fb7af294d5d9 92 * @endcode
Simon Cooksey 0:fb7af294d5d9 93 */
Simon Cooksey 0:fb7af294d5d9 94 template <typename T>
Simon Cooksey 0:fb7af294d5d9 95 class SafeBool : public SafeBool_::base {
Simon Cooksey 0:fb7af294d5d9 96 public:
Simon Cooksey 0:fb7af294d5d9 97 /**
Simon Cooksey 0:fb7af294d5d9 98 * Bool operator implementation, derived class has to provide bool toBool() const function.
Simon Cooksey 0:fb7af294d5d9 99 */
Simon Cooksey 0:fb7af294d5d9 100 operator BoolType_t() const {
Simon Cooksey 0:fb7af294d5d9 101 return (static_cast<const T*>(this))->toBool()
Simon Cooksey 0:fb7af294d5d9 102 ? &SafeBool<T>::trueTag : 0;
Simon Cooksey 0:fb7af294d5d9 103 }
Simon Cooksey 0:fb7af294d5d9 104 };
Simon Cooksey 0:fb7af294d5d9 105
Simon Cooksey 0:fb7af294d5d9 106 /**
Simon Cooksey 0:fb7af294d5d9 107 * Avoid conversion to bool between different classes.
Simon Cooksey 0:fb7af294d5d9 108 */
Simon Cooksey 0:fb7af294d5d9 109 template <typename T, typename U>
Simon Cooksey 0:fb7af294d5d9 110 void operator==(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
Simon Cooksey 0:fb7af294d5d9 111 lhs.invalidTag();
Simon Cooksey 0:fb7af294d5d9 112 // return false;
Simon Cooksey 0:fb7af294d5d9 113 }
Simon Cooksey 0:fb7af294d5d9 114
Simon Cooksey 0:fb7af294d5d9 115 /**
Simon Cooksey 0:fb7af294d5d9 116 * Avoid conversion to bool between different classes.
Simon Cooksey 0:fb7af294d5d9 117 */
Simon Cooksey 0:fb7af294d5d9 118 template <typename T,typename U>
Simon Cooksey 0:fb7af294d5d9 119 void operator!=(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
Simon Cooksey 0:fb7af294d5d9 120 lhs.invalidTag();
Simon Cooksey 0:fb7af294d5d9 121 // return false;
Simon Cooksey 0:fb7af294d5d9 122 }
Simon Cooksey 0:fb7af294d5d9 123
Simon Cooksey 0:fb7af294d5d9 124 #endif /* BLE_API_SAFE_BOOL_H_ */