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Fork of BLE_API by Bluetooth Low Energy

ble/SafeBool.h@1114:04913cb9706e, 2016-01-11 (annotated)

Committer:
vcoubard
Date:
Mon Jan 11 08:52:00 2016 +0000
Revision:
1114:04913cb9706e
Parent:
948:1bb402105289 
Synchronized with git rev 4af295ab

Author: Vincent Coubard

version v2.3.0

Who changed what in which revision?

UserRevisionLine numberNew contents of line
rgrover1 948:1bb402105289 1 /* mbed Microcontroller Library
rgrover1 948:1bb402105289 2 * Copyright (c) 2006-2013 ARM Limited
rgrover1 948:1bb402105289 3 *
rgrover1 948:1bb402105289 4 * Licensed under the Apache License, Version 2.0 (the "License");
rgrover1 948:1bb402105289 5 * you may not use this file except in compliance with the License.
rgrover1 948:1bb402105289 6 * You may obtain a copy of the License at
rgrover1 948:1bb402105289 7 *
rgrover1 948:1bb402105289 8 * http://www.apache.org/licenses/LICENSE-2.0
rgrover1 948:1bb402105289 9 *
rgrover1 948:1bb402105289 10 * Unless required by applicable law or agreed to in writing, software
rgrover1 948:1bb402105289 11 * distributed under the License is distributed on an "AS IS" BASIS,
rgrover1 948:1bb402105289 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
rgrover1 948:1bb402105289 13 * See the License for the specific language governing permissions and
rgrover1 948:1bb402105289 14 * limitations under the License.
rgrover1 948:1bb402105289 15 */
rgrover1 948:1bb402105289 16
rgrover1 948:1bb402105289 17 #ifndef BLE_API_SAFE_BOOL_H_
rgrover1 948:1bb402105289 18 #define BLE_API_SAFE_BOOL_H_
rgrover1 948:1bb402105289 19
rgrover1 948:1bb402105289 20 //safe bool idiom, see : http://www.artima.com/cppsource/safebool.html
rgrover1 948:1bb402105289 21
rgrover1 948:1bb402105289 22 namespace SafeBool_ {
rgrover1 948:1bb402105289 23 /**
rgrover1 948:1bb402105289 24 * @brief Base class for all intances of SafeBool,
rgrover1 948:1bb402105289 25 * This base class reduce instantiation of trueTag function
rgrover1 948:1bb402105289 26 */
rgrover1 948:1bb402105289 27 class base {
rgrover1 948:1bb402105289 28 template<typename>
rgrover1 948:1bb402105289 29 friend class SafeBool;
rgrover1 948:1bb402105289 30
rgrover1 948:1bb402105289 31 protected:
rgrover1 948:1bb402105289 32 //the bool type is a pointer to method which can be used in boolean context
rgrover1 948:1bb402105289 33 typedef void (base::*BoolType_t)() const;
rgrover1 948:1bb402105289 34
rgrover1 948:1bb402105289 35 // non implemented call, use to disallow conversion between unrelated types
rgrover1 948:1bb402105289 36 void invalidTag() const;
rgrover1 948:1bb402105289 37
rgrover1 948:1bb402105289 38 // member function which indicate true value
rgrover1 948:1bb402105289 39 void trueTag() const {}
rgrover1 948:1bb402105289 40 };
rgrover1 948:1bb402105289 41
rgrover1 948:1bb402105289 42
rgrover1 948:1bb402105289 43 }
rgrover1 948:1bb402105289 44
rgrover1 948:1bb402105289 45 /**
rgrover1 948:1bb402105289 46 * @brief template class SafeBool use CRTP to made boolean conversion easy and correct.
rgrover1 948:1bb402105289 47 * Derived class should implement the function bool toBool() const to make this work. Inheritance
rgrover1 948:1bb402105289 48 * should be public.
rgrover1 948:1bb402105289 49 *
rgrover1 948:1bb402105289 50 * @tparam T Type of the derived class
rgrover1 948:1bb402105289 51 *
rgrover1 948:1bb402105289 52 * \code
rgrover1 948:1bb402105289 53 *
rgrover1 948:1bb402105289 54 * class A : public SafeBool<A> {
rgrover1 948:1bb402105289 55 * public:
rgrover1 948:1bb402105289 56 *
rgrover1 948:1bb402105289 57 * // boolean conversion
rgrover1 948:1bb402105289 58 * bool toBool() {
rgrover1 948:1bb402105289 59 *
rgrover1 948:1bb402105289 60 * }
rgrover1 948:1bb402105289 61 * };
rgrover1 948:1bb402105289 62 *
rgrover1 948:1bb402105289 63 * class B : public SafeBool<B> {
rgrover1 948:1bb402105289 64 * public:
rgrover1 948:1bb402105289 65 *
rgrover1 948:1bb402105289 66 * // boolean conversion
rgrover1 948:1bb402105289 67 * bool toBool() const {
rgrover1 948:1bb402105289 68 *
rgrover1 948:1bb402105289 69 * }
rgrover1 948:1bb402105289 70 * };
rgrover1 948:1bb402105289 71 *
rgrover1 948:1bb402105289 72 * A a;
rgrover1 948:1bb402105289 73 * B b;
rgrover1 948:1bb402105289 74 *
rgrover1 948:1bb402105289 75 * // will compile
rgrover1 948:1bb402105289 76 * if(a) {
rgrover1 948:1bb402105289 77 *
rgrover1 948:1bb402105289 78 * }
rgrover1 948:1bb402105289 79 *
rgrover1 948:1bb402105289 80 * // compilation error
rgrover1 948:1bb402105289 81 * if(a == b) {
rgrover1 948:1bb402105289 82 *
rgrover1 948:1bb402105289 83 * }
rgrover1 948:1bb402105289 84 *
rgrover1 948:1bb402105289 85 *
rgrover1 948:1bb402105289 86 * \endcode
rgrover1 948:1bb402105289 87 */
rgrover1 948:1bb402105289 88 template <typename T>
rgrover1 948:1bb402105289 89 class SafeBool : public SafeBool_::base {
rgrover1 948:1bb402105289 90 public:
rgrover1 948:1bb402105289 91 /**
rgrover1 948:1bb402105289 92 * bool operator implementation, derived class has to provide bool toBool() const function.
rgrover1 948:1bb402105289 93 */
rgrover1 948:1bb402105289 94 operator BoolType_t() const {
rgrover1 948:1bb402105289 95 return (static_cast<const T*>(this))->toBool()
rgrover1 948:1bb402105289 96 ? &SafeBool<T>::trueTag : 0;
rgrover1 948:1bb402105289 97 }
rgrover1 948:1bb402105289 98 };
rgrover1 948:1bb402105289 99
rgrover1 948:1bb402105289 100 //Avoid conversion to bool between different classes
rgrover1 948:1bb402105289 101 template <typename T, typename U>
rgrover1 948:1bb402105289 102 void operator==(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
rgrover1 948:1bb402105289 103 lhs.invalidTag();
rgrover1 948:1bb402105289 104 // return false;
rgrover1 948:1bb402105289 105 }
rgrover1 948:1bb402105289 106
rgrover1 948:1bb402105289 107 //Avoid conversion to bool between different classes
rgrover1 948:1bb402105289 108 template <typename T,typename U>
rgrover1 948:1bb402105289 109 void operator!=(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
rgrover1 948:1bb402105289 110 lhs.invalidTag();
rgrover1 948:1bb402105289 111 // return false;
rgrover1 948:1bb402105289 112 }
rgrover1 948:1bb402105289 113
rgrover1 948:1bb402105289 114 #endif /* BLE_API_SAFE_BOOL_H_ */