BLE - add static interface helper.

Author: pan-

features/FEATURE_BLE/ble/common/StaticInterface.h

@@ -0,0 +1,55 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2019 ARM Limited
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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_COMMON_STATICINTERFACE_H
+#define BLE_COMMON_STATICINTERFACE_H
+
+namespace ble {
+
+/**
+ * Static Interface helper class.
+ *
+ * @tparam Impl Implementation class.
+ * @tparam Interface Interface template
+ */
+template <typename Impl, template<typename> class Interface>
+struct StaticInterface
+{
+    /**
+     * @return A pointer to the implementation class.
+     */
+    Impl* impl()
+    {
+        return static_cast<Impl*>(this);
+    }
+
+    /**
+     * @return A pointer to the implementation class.
+     */
+    const Impl* impl() const
+    {
+        return static_cast<const Impl*>(this);
+    }
+
+private:
+    StaticInterface() {}
+    friend Interface<Impl>;
+};
+
+} // namespace ble
+
+#endif //BLE_COMMON_STATICINTERFACE_H