Diff: microbit/microbit-dal/BLE_API/ble/SafeBool.h

Revision:

0:b9164b348919

diff -r 000000000000 -r b9164b348919 microbit/microbit-dal/BLE_API/ble/SafeBool.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/microbit/microbit-dal/BLE_API/ble/SafeBool.h	Mon Oct 17 12:41:20 2016 +0000
@@ -0,0 +1,114 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2013 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef BLE_API_SAFE_BOOL_H_
+#define BLE_API_SAFE_BOOL_H_
+
+//safe bool idiom, see : http://www.artima.com/cppsource/safebool.html
+
+namespace SafeBool_ {
+/**
+ * @brief Base class for all intances of SafeBool, 
+ * This base class reduce instantiation of trueTag function
+ */
+class base {
+  template<typename>
+  friend class SafeBool;
+
+protected:
+    //the bool type is a pointer to method which can be used in boolean context
+  typedef void (base::*BoolType_t)() const;
+
+  // non implemented call, use to disallow conversion between unrelated types 
+  void invalidTag() const;
+
+  // member function which indicate true value
+  void trueTag() const {}
+};
+
+
+}
+
+/**
+ * @brief template class SafeBool use CRTP to made boolean conversion easy and correct.
+ * Derived class should implement the function bool toBool() const to make this work. Inheritance 
+ * should be public.
+ *
+ * @tparam T Type of the derived class
+ * 
+ * \code 
+ * 
+ * class A : public SafeBool<A> { 
+ * public:
+ * 
+ *      // boolean conversion
+ *      bool toBool() { 
+ *      
+ *      }  
+ * };
+ * 
+ * class B : public SafeBool<B> { 
+ * public:
+ * 
+ *      // boolean conversion
+ *      bool toBool() const { 
+ *      
+ *      }  
+ * };
+ * 
+ * A a;
+ * B b;
+ * 
+ * // will compile 
+ * if(a) { 
+ * 
+ * }
+ * 
+ * // compilation error 
+ * if(a == b) { 
+ * 
+ * }
+ * 
+ * 
+ * \endcode
+ */
+template <typename T> 
+class SafeBool : public SafeBool_::base {
+public:
+  /** 
+   * bool operator implementation, derived class has to provide bool toBool() const function.
+   */
+  operator BoolType_t() const {
+    return (static_cast<const T*>(this))->toBool()
+      ? &SafeBool<T>::trueTag : 0;
+  }
+};
+
+//Avoid conversion to bool between different classes
+template <typename T, typename U>
+void operator==(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
+    lhs.invalidTag();
+//    return false;
+}
+
+//Avoid conversion to bool between different classes
+template <typename T,typename U>
+void operator!=(const SafeBool<T>& lhs,const SafeBool<U>& rhs) {
+  lhs.invalidTag();
+//  return false;
+}
+
+#endif /* BLE_API_SAFE_BOOL_H_ */
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