Diff: features/FEATURE_BLE/ble/SafeBool.h

Revision:

0:f269e3021894

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/features/FEATURE_BLE/ble/SafeBool.h	Sun Oct 23 15:10:02 2016 +0000
@@ -0,0 +1,124 @@
+/* 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 reduces 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_ */