Functional requirements:

• functionality and API equivalent to ROS2 C++ client library (C++ client library has most advanced feature set right now)
  • Reference - C++ client library: rclcpp
• functionality equivalent to ROS2 C++ client library (C++ client library user code depends on idl generator)
  • Reference - C++ idl generator: rosidl_generator_cpp
• functionality to support building D client library packages
  • Reference - C++ ament build integration: ament_cmake

Non-functional requirements:

• compiler: LDC (D compiler comparison: most platforms and architectures supported)
• integration of tool based static code analysis into build tool (other client libraries aim at integration of tools extensively)
  • C++ client library reference: integration of CppCheck (common code flaw checking) into Ament (non-/CMake based) built environment for C++ client library ament_cppcheck / ament_cmake_cppcheck
  • C++ client library reference: integration of CppLint and clang format (style guide checking) into Ament (non-/CMake based) build environment for C++ client library ament_cpplint / ament_cmake_cpplint / ament_clang_format
  • D: D-Scanner
• design by contract (C++ does not support this but will probably support it if ROS2 begins to support C++17)
• unit tests (other client libraries aim at extensive unit testing as well)
  • C++ client library reference: rclcpp/test
• rmw (ROS2 middleware) integration tests (C++ client library aims at extensive middleware integration testing as well)
  • C++ client library reference: system_tests/test_communication
  • test of communiaction (publish/subscribe/request/response)
  • test with all primitive and builtin types
  • test with every available rmw implementation
• security tests (C++ client library aims at extensive security testing):
  • C++ client library reference: system_tests/test_security)
  • test nodes, publishers and subscribers with DDS-Security
• API tests (other client libraries like C++ client library aims at extensive API testing as well)
  • C++ client library API tests
  • Reference - ROS2 launch (test runner): launch
  • Reference - Helper scripts for tests using the launch tool: launch_testing
• code coverage (usually web services like coveralls.io which support statement coverage analysis are used to analyze open source ROS2 packages)
  • coverage type: statement coverage
  • web service based coverage analysis for D could be executed with coveralls.io via doveralls
• priorization of software quality attributes (over the mid to long term I expect the following priorization for C/C++ ROS2 packages)
  • security
  • reliability
  • performance

ROS2 Architecture

How a client library (here: C++) fits into the big picture.

• A ROS2 client library ({client libraries}) interfaces the rcl. The rcl is the interface and implementation of client library functionality which is common for all client libraries. It is implemented in C. The rmw is implemented in C as well.
• For every language specific client library a generator for lanuage specific ROS2 interface is required, e.g. rosidl_generator_cpp generates the ROS2 interfaces in C++ (not shown in the diagram).
• In the example below the {DDS vendor} (Fast-RTPS) and {rmw impl} (rmw_fastrtps_cpp) are both implemented in C++. However these layers are independent of the client library and there is no need to implement them in D.

ROS-I Consortium 2017 Presentation: Looking forward to ROS2