Diff: mbed-os/features/FEATURE_BLE/ble/SafeBool.h

Revision:

0:9fca2b23d0ba

diff -r 000000000000 -r 9fca2b23d0ba mbed-os/features/FEATURE_BLE/ble/SafeBool.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os/features/FEATURE_BLE/ble/SafeBool.h	Sat Feb 23 12:13:36 2019 +0000
@@ -0,0 +1,154 @@
+/* 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 */
+
+/**
+ * @file
+ * @addtogroup ble
+ * @{
+ * @addtogroup common
+ * @{
+ */
+
+/**
+ *  Private namespace used to host details of the SafeBool implementation.
+ */
+namespace SafeBool_ {
+/**
+ * Base class of all SafeBool instances.
+ *
+ * This nontemplate base class exists to reduce the number of instantiation of
+ * the trueTag function.
+ */
+class base {
+  template<typename>
+  friend class SafeBool;
+
+protected:
+    /**
+     * The bool type is a pointer to method that can be used in boolean context.
+     */
+    typedef void (base::*BoolType_t)() const;
+
+    /**
+     * Nonimplemented call, use to disallow conversion between unrelated types.
+     */
+    void invalidTag() const;
+
+    /**
+     * Special member function that indicates a true value.
+     */
+    void trueTag() const {}
+};
+
+
+}
+
+/**
+ * Safe conversion of objects in boolean context.
+ *
+ * Classes wanting evaluation of their instances in boolean context must derive
+ * publicly from this class rather than implementing the easy to misuse
+ * operator bool().
+ *
+ * Descendant classes must implement the function bool toBool() const to enable
+ * the safe conversion in boolean context.
+ *
+ * @tparam T Type of the derived class
+ *
+ * @code
+ *
+ * class A : public SafeBool<A> {
+ * public:
+ *
+ *      // boolean conversion
+ *      bool toBool() const {
+ *
+ *      }
+ * };
+ *
+ * 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 must provide a 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.
+ *
+ * @important Will generate a compile time error if instantiated.
+ */
+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.
+ *
+ * @important Will generate a compile time error if instantiated.
+ */
+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_ */