[Backport Foxy] Add scope_exit helper. (#78)

CMakeLists.txt

@@ -70,6 +70,9 @@ if(BUILD_TESTING)
   )
   ament_target_dependencies(test_get_env rcutils)
 
+  ament_add_gtest(test_scope_exit test/test_scope_exit.cpp)
+  target_link_libraries(test_scope_exit ${PROJECT_NAME})
+
   ament_add_gtest(test_split test/test_split.cpp)
 
   ament_add_gtest(test_filesystem_helper test/test_filesystem_helper.cpp

include/rcpputils/scope_exit.hpp

@@ -0,0 +1,68 @@
+// Copyright 2015-2020 Open Source Robotics Foundation, Inc.
+//
+// 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 RCPPUTILS__SCOPE_EXIT_HPP_
+#define RCPPUTILS__SCOPE_EXIT_HPP_
+
+#include <utility>
+
+#include "rcutils/macros.h"
+
+namespace rcpputils
+{
+
+template<typename CallableT>
+struct scope_exit final
+{
+  explicit scope_exit(CallableT && callable)
+  : callable_(std::forward<CallableT>(callable))
+  {
+  }
+
+  scope_exit(const scope_exit &) = delete;
+  scope_exit(scope_exit &&) = default;
+
+  scope_exit & operator=(const scope_exit &) = delete;
+  scope_exit & operator=(scope_exit &&) = default;
+
+  ~scope_exit()
+  {
+    if (!cancelled_) {
+      callable_();
+    }
+  }
+
+  void cancel()
+  {
+    cancelled_ = true;
+  }
+
+private:
+  CallableT callable_;
+  bool cancelled_{false};
+};
+
+template<typename CallableT>
+scope_exit<CallableT>
+make_scope_exit(CallableT && callable)
+{
+  return scope_exit<CallableT>(std::forward<CallableT>(callable));
+}
+
+}  // namespace rcpputils
+
+#define RCPPUTILS_SCOPE_EXIT(code) \
+  auto RCUTILS_JOIN(scope_exit_, __LINE__) = rcpputils::make_scope_exit([&]() {code;})
+
+#endif  // RCPPUTILS__SCOPE_EXIT_HPP_

test/test_scope_exit.cpp

@@ -0,0 +1,64 @@
+// Copyright 2020 Open Source Robotics Foundation, Inc.
+//
+// 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.
+
+#include <gtest/gtest.h>
+
+#include "rcpputils/scope_exit.hpp"
+
+TEST(test_scope_exit, should_run) {
+  bool called = false;
+
+  {
+    auto on_exit =
+      rcpputils::make_scope_exit(
+      [&called]() {
+        called = true;
+      });
+    (void)on_exit;
+  }
+
+  EXPECT_TRUE(called);
+}
+
+TEST(test_scope_exit, should_not_run) {
+  bool called = false;
+
+  {
+    auto on_exit =
+      rcpputils::make_scope_exit(
+      [&called]() {
+        called = true;
+      });
+    on_exit.cancel();
+  }
+
+  EXPECT_FALSE(called);
+}
+
+TEST(test_scope_exit, code_types) {
+  auto code = []() {};
+  rcpputils::make_scope_exit(code);
+
+  const auto const_code = []() {};
+  rcpputils::make_scope_exit(const_code);
+
+  struct NonCopyableCode
+  {
+    NonCopyableCode() = default;
+    NonCopyableCode(const NonCopyableCode &) = delete;
+    NonCopyableCode(NonCopyableCode &&) = default;
+    void operator()() {}
+  };
+  rcpputils::make_scope_exit(NonCopyableCode());
+}