Neil Johnson / microbit-ARMBand

Official Sheffield ARMBand micro:bit program

microbit/microbit-dal/BLE_API/ble/SafeBool.h@0:b9164b348919, 2016-10-17 (annotated)

Committer:
MrBedfordVan
Date:
Mon Oct 17 12:41:20 2016 +0000
Revision:
0:b9164b348919
Official Sheffield ARMBand Micro:bit program

Who changed what in which revision?

UserRevisionLine numberNew contents of line
MrBedfordVan 0:b9164b348919 1 /* mbed Microcontroller Library
MrBedfordVan 0:b9164b348919 2 * Copyright (c) 2006-2013 ARM Limited
MrBedfordVan 0:b9164b348919 3 *
MrBedfordVan 0:b9164b348919 4 * Licensed under the Apache License, Version 2.0 (the "License");
MrBedfordVan 0:b9164b348919 5 * you may not use this file except in compliance with the License.
MrBedfordVan 0:b9164b348919 6 * You may obtain a copy of the License at
MrBedfordVan 0:b9164b348919 7 *
MrBedfordVan 0:b9164b348919 8 * http://www.apache.org/licenses/LICENSE-2.0
MrBedfordVan 0:b9164b348919 9 *
MrBedfordVan 0:b9164b348919 10 * Unless required by applicable law or agreed to in writing, software
MrBedfordVan 0:b9164b348919 11 * distributed under the License is distributed on an "AS IS" BASIS,
MrBedfordVan 0:b9164b348919 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
MrBedfordVan 0:b9164b348919 13 * See the License for the specific language governing permissions and
MrBedfordVan 0:b9164b348919 14 * limitations under the License.
MrBedfordVan 0:b9164b348919 15 */
MrBedfordVan 0:b9164b348919 16
MrBedfordVan 0:b9164b348919 17 #ifndef BLE_API_SAFE_BOOL_H_
MrBedfordVan 0:b9164b348919 18 #define BLE_API_SAFE_BOOL_H_
MrBedfordVan 0:b9164b348919 19
MrBedfordVan 0:b9164b348919 20 //safe bool idiom, see : http://www.artima.com/cppsource/safebool.html
MrBedfordVan 0:b9164b348919 21
MrBedfordVan 0:b9164b348919 22 namespace SafeBool_ {
MrBedfordVan 0:b9164b348919 23 /**
MrBedfordVan 0:b9164b348919 24 * @brief Base class for all intances of SafeBool,
MrBedfordVan 0:b9164b348919 25 * This base class reduce instantiation of trueTag function
MrBedfordVan 0:b9164b348919 26 */
MrBedfordVan 0:b9164b348919 27 class base {
MrBedfordVan 0:b9164b348919 28 template<typename>
MrBedfordVan 0:b9164b348919 29 friend class SafeBool;
MrBedfordVan 0:b9164b348919 30
MrBedfordVan 0:b9164b348919 31 protected:
MrBedfordVan 0:b9164b348919 32 //the bool type is a pointer to method which can be used in boolean context
MrBedfordVan 0:b9164b348919 33 typedef void (base::*BoolType_t)() const;
MrBedfordVan 0:b9164b348919 34
MrBedfordVan 0:b9164b348919 35 // non implemented call, use to disallow conversion between unrelated types
MrBedfordVan 0:b9164b348919 36 void invalidTag() const;
MrBedfordVan 0:b9164b348919 37
MrBedfordVan 0:b9164b348919 38 // member function which indicate true value
MrBedfordVan 0:b9164b348919 39 void trueTag() const {}
MrBedfordVan 0:b9164b348919 40 };
MrBedfordVan 0:b9164b348919 41
MrBedfordVan 0:b9164b348919 42
MrBedfordVan 0:b9164b348919 43 }
MrBedfordVan 0:b9164b348919 44
MrBedfordVan 0:b9164b348919 45 /**
MrBedfordVan 0:b9164b348919 46 * @brief template class SafeBool use CRTP to made boolean conversion easy and correct.
MrBedfordVan 0:b9164b348919 47 * Derived class should implement the function bool toBool() const to make this work. Inheritance
MrBedfordVan 0:b9164b348919 48 * should be public.
MrBedfordVan 0:b9164b348919 49 *
MrBedfordVan 0:b9164b348919 50 * @tparam T Type of the derived class
MrBedfordVan 0:b9164b348919 51 *
MrBedfordVan 0:b9164b348919 52 * \code
MrBedfordVan 0:b9164b348919 53 *
MrBedfordVan 0:b9164b348919 54 * class A : public SafeBool<A> {
MrBedfordVan 0:b9164b348919 55 * public:
MrBedfordVan 0:b9164b348919 56 *
MrBedfordVan 0:b9164b348919 57 * // boolean conversion
MrBedfordVan 0:b9164b348919 58 * bool toBool() {
MrBedfordVan 0:b9164b348919 59 *
MrBedfordVan 0:b9164b348919 60 * }
MrBedfordVan 0:b9164b348919 61 * };
MrBedfordVan 0:b9164b348919 62 *
MrBedfordVan 0:b9164b348919 63 * class B : public SafeBool<B> {
MrBedfordVan 0:b9164b348919 64 * public:
MrBedfordVan 0:b9164b348919 65 *
MrBedfordVan 0:b9164b348919 66 * // boolean conversion
MrBedfordVan 0:b9164b348919 67 * bool toBool() const {
MrBedfordVan 0:b9164b348919 68 *
MrBedfordVan 0:b9164b348919 69 * }
MrBedfordVan 0:b9164b348919 70 * };
MrBedfordVan 0:b9164b348919 71 *
MrBedfordVan 0:b9164b348919 72 * A a;
MrBedfordVan 0:b9164b348919 73 * B b;
MrBedfordVan 0:b9164b348919 74 *
MrBedfordVan 0:b9164b348919 75 * // will compile
MrBedfordVan 0:b9164b348919 76 * if(a) {
MrBedfordVan 0:b9164b348919 77 *
MrBedfordVan 0:b9164b348919 78 * }
MrBedfordVan 0:b9164b348919 79 *
MrBedfordVan 0:b9164b348919 80 * // compilation error
MrBedfordVan 0:b9164b348919 81 * if(a == b) {
MrBedfordVan 0:b9164b348919 82 *
MrBedfordVan 0:b9164b348919 83 * }
MrBedfordVan 0:b9164b348919 84 *
MrBedfordVan 0:b9164b348919 85 *
MrBedfordVan 0:b9164b348919 86 * \endcode
MrBedfordVan 0:b9164b348919 87 */
MrBedfordVan 0:b9164b348919 88 template <typename T>
MrBedfordVan 0:b9164b348919 89 class SafeBool : public SafeBool_::base {
MrBedfordVan 0:b9164b348919 90 public:
MrBedfordVan 0:b9164b348919 91 /**
MrBedfordVan 0:b9164b348919 92 * bool operator implementation, derived class has to provide bool toBool() const function.
MrBedfordVan 0:b9164b348919 93 */
MrBedfordVan 0:b9164b348919 94 operator BoolType_t() const {
MrBedfordVan 0:b9164b348919 95 return (static_cast<const T*>(this))->toBool()
MrBedfordVan 0:b9164b348919 96 ? &SafeBool<T>::trueTag : 0;
MrBedfordVan 0:b9164b348919 97 }
MrBedfordVan 0:b9164b348919 98 };
MrBedfordVan 0:b9164b348919 99
MrBedfordVan 0:b9164b348919 100 //Avoid conversion to bool between different classes
MrBedfordVan 0:b9164b348919 101 template <typename T, typename U>
MrBedfordVan 0:b9164b348919 102 void operator==(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
MrBedfordVan 0:b9164b348919 103 lhs.invalidTag();
MrBedfordVan 0:b9164b348919 104 // return false;
MrBedfordVan 0:b9164b348919 105 }
MrBedfordVan 0:b9164b348919 106
MrBedfordVan 0:b9164b348919 107 //Avoid conversion to bool between different classes
MrBedfordVan 0:b9164b348919 108 template <typename T,typename U>
MrBedfordVan 0:b9164b348919 109 void operator!=(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
MrBedfordVan 0:b9164b348919 110 lhs.invalidTag();
MrBedfordVan 0:b9164b348919 111 // return false;
MrBedfordVan 0:b9164b348919 112 }
MrBedfordVan 0:b9164b348919 113
MrBedfordVan 0:b9164b348919 114 #endif /* BLE_API_SAFE_BOOL_H_ */