mirror of https://github.com/ARMmbed/mbed-os.git
155 lines
3.2 KiB
C++
155 lines
3.2 KiB
C++
/* mbed Microcontroller Library
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* Copyright (c) 2006-2013 ARM Limited
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef BLE_API_SAFE_BOOL_H_
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#define BLE_API_SAFE_BOOL_H_
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/* Safe bool idiom, see: http://www.artima.com/cppsource/safebool.html */
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/**
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* @file
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* @addtogroup ble
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* @{
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* @addtogroup common
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* @{
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*/
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/**
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* Private namespace used to host details of the SafeBool implementation.
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*/
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namespace SafeBool_ {
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/**
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* Base class of all SafeBool instances.
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*
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* This nontemplate base class exists to reduce the number of instantiation of
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* the trueTag function.
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*/
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class base {
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template<typename>
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friend class SafeBool;
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protected:
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/**
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* The bool type is a pointer to method that can be used in boolean context.
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*/
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typedef void (base::*BoolType_t)() const;
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/**
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* Nonimplemented call, use to disallow conversion between unrelated types.
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*/
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void invalidTag() const;
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/**
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* Special member function that indicates a true value.
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*/
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void trueTag() const {}
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};
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}
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/**
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* Safe conversion of objects in boolean context.
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*
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* Classes wanting evaluation of their instances in boolean context must derive
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* publicly from this class rather than implementing the easy to misuse
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* operator bool().
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*
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* Descendant classes must implement the function bool toBool() const to enable
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* the safe conversion in boolean context.
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*
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* @tparam T Type of the derived class
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*
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* @code
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*
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* class A : public SafeBool<A> {
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* public:
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*
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* // boolean conversion
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* bool toBool() const {
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*
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* }
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* };
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*
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* class B : public SafeBool<B> {
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* public:
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*
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* // boolean conversion
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* bool toBool() const {
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*
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* }
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* };
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*
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* A a;
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* B b;
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*
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* // will compile
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* if(a) {
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*
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* }
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*
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* // compilation error
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* if(a == b) {
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*
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* }
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* @endcode
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*/
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template <typename T>
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class SafeBool : public SafeBool_::base {
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public:
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/**
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* Bool operator implementation, derived class must provide a bool
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* toBool() const function.
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*/
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operator BoolType_t() const
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{
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return (static_cast<const T*>(this))->toBool()
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? &SafeBool<T>::trueTag : 0;
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}
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};
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/**
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* Avoid conversion to bool between different classes.
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*
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* @attention Will generate a compile time error if instantiated.
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*/
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template <typename T, typename U>
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void operator==(const SafeBool<T>& lhs,const SafeBool<U>& rhs)
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{
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lhs.invalidTag();
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// return false;
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}
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/**
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* Avoid conversion to bool between different classes.
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*
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* @attention Will generate a compile time error if instantiated.
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*/
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template <typename T,typename U>
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void operator!=(const SafeBool<T>& lhs,const SafeBool<U>& rhs)
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{
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lhs.invalidTag();
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// return false;
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}
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/**
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* @}
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* @}
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*/
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#endif /* BLE_API_SAFE_BOOL_H_ */
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