utility: add defer (#110)

include/dsn/utility/defer.h

@@ -0,0 +1,69 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Microsoft Corporation
+ *
+ * -=- Robust Distributed System Nucleus (rDSN) -=-
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+namespace dsn {
+
+// `defer` is an useful util to implement RAII in golang, much alike
+// `try...finally...` in java. In C++ we used to implement an RAII class
+// wrapping around the resource:
+//
+// ```cpp
+// struct object_raii
+// {
+//   object_raii() {
+//     _obj = c_object_new();
+//   }
+//   ~object_raii() {
+//     c_object_free(_obj);
+//   }
+// private:
+//   c_object *_obj;
+// };
+// ```
+//
+// Now with `defer`, things will be simplified:
+//
+// ```cpp
+// c_object *obj = c_object_new();
+// auto cleanup = dsn::defer([obj]() { c_object_free(obj); });
+// ```
+
+template <typename Func>
+struct deferred_action
+{
+    explicit deferred_action(Func &&func) noexcept : _func(std::move(func)) {}
+    ~deferred_action() { _func(); }
+private:
+    Func _func;
+};
+
+template <typename Func>
+inline deferred_action<Func> defer(Func &&func)
+{
+    return deferred_action<Func>(std::forward<Func>(func));
+}
+
+} // namespace dsn