Cannot register node that takes interface as extra parameter

[gvallicrosa]

Describe the bug

Using release 4.6.2.

I was trying to register a node that depends on an interface in its constructor:

#include <behaviortree_cpp/bt_factory.h>

// interface
struct IMotor {
  virtual void doMove() = 0;
};

// implementation
struct LinearMotor : public IMotor {
  void doMove() override {}
};

// node using interface
class PathFollow : public BT::StatefulActionNode {
 public:
  PathFollow(const std::string& name, const BT::NodeConfig& config, IMotor& motor)
      : BT::StatefulActionNode(name, config), imotor_(motor) {}
  static BT::PortsList providedPorts() { return {}; }
  BT::NodeStatus onStart() override { return BT::NodeStatus::SUCCESS; }
  BT::NodeStatus onRunning() override { return BT::NodeStatus::SUCCESS; }
  void onHalted() override {}

 private:
  IMotor& imotor_;
};

int main() {
  LinearMotor motor;
  BT::BehaviorTreeFactory factory;
  factory.registerNodeType<PathFollow>("PathFollow", motor);
  factory.registerNodeType<PathFollow>("PathFollow", PathFollow::providedPorts(), motor);
  factory.registerNodeType<PathFollow, LinearMotor&>("PathFollow", PathFollow::providedPorts(), motor);
  factory.registerNodeType<PathFollow, IMotor&>("PathFollow", PathFollow::providedPorts(), motor);
}

Trying different ways to register the node, none of them compile. Is there a way to use an interface as an extra argument? Already checked the tutorial 8 and normal examples with values compile without problems.

Here is the compilation output:

In file included from /interface.cc:1:
/usr/local/include/behaviortree_cpp/bt_factory.h: In instantiation of ‘void BT::BehaviorTreeFactory::registerNodeType(const string&, ExtraArgs ...) [with T = PathFollow; ExtraArgs = {LinearMotor}; std::string = std::__cxx11::basic_string<char>]’:
/interface.cc:30:39:   required from here
/usr/local/include/behaviortree_cpp/bt_factory.h:379:21: error: static assertion failed: [registerNode]: since you have a static method providedPorts(),
you MUST add a constructor with signature:
(const std::string&, const NodeConfig&)

  379 |       static_assert(!(has_static_ports_list && !param_constructable),
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/behaviortree_cpp/bt_factory.h:379:21: note: ‘((!(bool)has_static_ports_list) || ((bool)param_constructable))’ evaluates to false
/usr/local/include/behaviortree_cpp/bt_factory.h: In instantiation of ‘void BT::BehaviorTreeFactory::registerNodeType(const string&, const PortsList&, ExtraArgs ...) [with T = PathFollow; ExtraArgs = {LinearMotor}; std::string = std::__cxx11::basic_string<char>; BT::PortsList = std::unordered_map<std::__cxx11::basic_string<char>, BT::PortInfo>]’:
/interface.cc:31:39:   required from here
/usr/local/include/behaviortree_cpp/bt_factory.h:343:41: error: static assertion failed: [registerNode]: the registered class must have at least one of these two constructors:
  (const std::string&, const NodeConfig&) or (const std::string&)
Check also if the constructor is public!)
  343 |     static_assert(default_constructable || param_constructable,
      |                   ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/behaviortree_cpp/bt_factory.h:343:41: note: ‘(((bool)default_constructable) || ((bool)param_constructable))’ evaluates to false
/usr/local/include/behaviortree_cpp/bt_factory.h: In instantiation of ‘void BT::BehaviorTreeFactory::registerNodeType(const string&, const PortsList&, ExtraArgs ...) [with T = PathFollow; ExtraArgs = {IMotor&}; std::string = std::__cxx11::basic_string<char>; BT::PortsList = std::unordered_map<std::__cxx11::basic_string<char>, BT::PortInfo>]’:
/interface.cc:33:48:   required from here
/usr/local/include/behaviortree_cpp/bt_factory.h:349:67: error: cannot allocate an object of abstract type ‘IMotor’
  349 |     registerBuilder(CreateManifest<T>(ID, ports), CreateBuilder<T>(args...));
      |                                                   ~~~~~~~~~~~~~~~~^~~~~~~~~
/interface.cc:4:8: note:   because the following virtual functions are pure within ‘IMotor’:
    4 | struct IMotor {
      |        ^~~~~~
/interface.cc:5:16: note:     ‘virtual void IMotor::doMove()’
    5 |   virtual void doMove() = 0;
      |

This node should be "param_constructable" with the LinearMotor struct passed to it. Any guess on how to do it? Am I missing something basic?

[vincent-hui]

Perhaps you need to make your class PathFollow default_constructable.

[gvallicrosa]

But then I would have to pass the argument in an init function using a visitor as explained in the tutorial, but I would rather prefer to have everything on a single step. Also avoid pointers if possible,

[gvallicrosa]

If instead of using references, std::shared_ptr are used, then the code compiles correctly

#include <behaviortree_cpp/bt_factory.h>
#include <iostream>
#include <memory>

// interface
struct IMotor {
  virtual void doMove() = 0;
};

// implementation
struct LinearMotor : public IMotor {
  void doMove() override { std::cout << ">> doMove\n"; }
};

// node using interface
class PathFollow : public BT::StatefulActionNode {
public:
  PathFollow(const std::string &name, const BT::NodeConfig &config,
             std::shared_ptr<IMotor> motor)
      : BT::StatefulActionNode(name, config), imotor_(motor) {}
  static BT::PortsList providedPorts() { return {}; }
  BT::NodeStatus onStart() override {
    std::cout << "onStart\n";
    imotor_->doMove();
    return BT::NodeStatus::RUNNING;
  }
  BT::NodeStatus onRunning() override {
    std::cout << "onRunning\n";
    imotor_->doMove();
    return BT::NodeStatus::SUCCESS;
  }
  void onHalted() override {}

private:
  std::shared_ptr<IMotor> imotor_;
};

int main() {
  auto motor = std::make_shared<LinearMotor>();
  BT::BehaviorTreeFactory factory;
  factory.registerNodeType<PathFollow>("PathFollow", motor);

  auto tree =
      factory.createTreeFromText((" <root BTCPP_format=\"4\">"
                                  "  <BehaviorTree ID=\"MainTree\">"
                                  "    <Sequence name=\"root_sequence\">"
                                  "      <PathFollow name=\"path_follow\"/>"
                                  "    </Sequence>"
                                  "  </BehaviorTree>"
                                  "</root>"));
  tree.tickWhileRunning();
}

[facontidavide]

This compiles:

LinearMotor motor;
BT::BehaviorTreeFactory factory;
factory.registerNodeType<PathFollow>("PathFollow", std::ref(motor));

[gvallicrosa]

Thanks a lot. 🙇‍♂