subscriber callbacks bound to class methods do not compile

[tfoote]

It fails due to an inability to resolve an overloaded function.

/home/tfoote/work/ros2/tf3/install/include/rclcpp/function_traits.hpp:51:85: error: decltype cannot resolve address of overloaded function
       typename function_traits<decltype( & FunctionT::operator())>::arguments>::type;

The full error is here: https://gist.github.com/tfoote/17222805a01e7c05c3f1

[jacquelinekay]

Can you make this a test case in system_tests/test_rclcpp instead? (I meant to post this comment on the pull request in examples, sorry if that was confusing.)

[jacquelinekay]

Are you working on a fix for this right now? I will take a look if you're not actively working on it.

[tfoote]

@esteve found a workaround to use a lambda function. I'll add a unit test for it too.

[jacquelinekay]

You mean using a lambda function in the example? Or to make bound functions work as the input to create_subscription?

None of our tested rclcpp code so far uses std::bind. Any code that captures arguments does so using lambdas.

Playing around with this, I found another "workaround" that compiles:

std::function<void(const std_msgs::msg::String::SharedPtr)> callback = std::bind(&Chatter::chatterCallback, &chatter, std::placeholders::_1);
  auto sub = node->create_subscription<std_msgs::msg::String>(
    "chatter", callback, rmw_qos_profile_default);

Ideally we would support any valid callback signature for create_subscription, so I think we should do the necessary work to make your example compile.

[esteve]

@tfoote could you have a look at this branch and see if it works? Thanks.

https://github.com/ros2/rclcpp/tree/std_bind_function_traits

[esteve]

@tfoote I got your example compiling with my branch, I'll clean up the changes here and submit them for review.

[tfoote]

@esteve I can confirm that your branch works for me, but I see it's not a cross platform solution unfortunately :-(

[esteve]

@tfoote I got the workaround to compile on all three platforms in #183, I'll see if I can compile the std::bind test in ros2/system_tests#88

[tfoote]

fixed in #183