Example of extending a controller and changing the interface _without_ needing multiple inheritance.

extensible_controllers.cpp

///////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2017, Clearpath Robotics Inc.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//   * Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.
//   * Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in the
//     documentation and/or other materials provided with the distribution.
//   * Neither the name of hiDOF, Inc. nor the names of its
//     contributors may be used to endorse or promote products derived from
//     this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//////////////////////////////////////////////////////////////////////////////

#include <controller_manager_tests/extensible_controllers.h>

using namespace controller_manager_tests;

bool ExtensibleController::init(hardware_interface::RobotHW* robot_hw,
          ros::NodeHandle& root_nh, ros::NodeHandle& controller_nh)
{
  std::string vel_joint_name;
  controller_nh.getParam("velocity_joint", vel_joint_name);

  hardware_interface::VelocityJointInterface* joint_iface = robot_hw->get<hardware_interface::VelocityJointInterface>();
  joint_iface->getHandle(vel_joint_name);
  return true;
}

int ExtensibleController::helper()
{
  return 1;
}

void ExtensibleController::update(const ros::Time&, const ros::Duration&)
{
  // TODO: Publish this return value so that the test can validate it?
  int foo = helper();
}


bool DerivedController::init(hardware_interface::RobotHW* robot_hw,
                             ros::NodeHandle& root_nh, ros::NodeHandle& controller_nh)
{
  // First initialize the base controller.
  base_controller.reset(new ExtendingController());
  if (!base_controller->init(robot_hw, root_nh, controller_nh))
  {
    return false;
  }

  std::string eff_joint_name;
  controller_nh.getParam("effort_joint", eff_joint_name);

  hardware_interface::EffortJointInterface* joint_iface = robot_hw->get<hardware_interface::EffortJointInterface>();
  joint_iface->getHandle(eff_joint_name);
  return true;
}

void DerivedController::update(const ros::Time& t, const ros::Duration& d)
{
  base_controller->update(t, d);
}

int ExtendingController::helper()
{
  return 2;
}

PLUGINLIB_EXPORT_CLASS(controller_manager_tests::ExtensibleController, controller_interface::ControllerBase)
PLUGINLIB_EXPORT_CLASS(controller_manager_tests::DerivedController, controller_interface::ControllerBase)

extensible_controllers.h

///////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2017, Clearpath Robotics Inc.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//   * Redistributions of source code must retain the above copyright notice,
//     this list of conditions and the following disclaimer.
//   * Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in the
//     documentation and/or other materials provided with the distribution.
//   * Neither the name of hiDOF, Inc. nor the names of its
//     contributors may be used to endorse or promote products derived from
//     this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
//////////////////////////////////////////////////////////////////////////////

#ifndef CONTROLLER_MANAGER_TESTS_EXTENSIBLE_CONTROLLERS_H
#define CONTROLLER_MANAGER_TESTS_EXTENSIBLE_CONTROLLERS_H

#include <boost/scoped_ptr.hpp>
#include <controller_interface/multi_interface_controller.h>
#include <hardware_interface/joint_command_interface.h>
#include <pluginlib/class_list_macros.h>

namespace controller_manager_tests
{

/**
 * This controller supplies an intentional extension point in the form of the virtual
 * "helper" function that the update method calls.
 */
class ExtensibleController : public controller_interface::MultiInterfaceController<hardware_interface::VelocityJointInterface>
{
public:
  bool init(hardware_interface::RobotHW* robot_hw, ros::NodeHandle& root_nh, ros::NodeHandle& controller_nh);
  virtual int helper();
  void update(const ros::Time&, const ros::Duration&);
};

/**
 * The derived controller not only overrides the virtual helper method, it also adds an additional
 * hardware interface, in order to demonstrate the flexbility of this mechanism.
 */
class ExtendingController : public ExtensibleController
{
  friend class DerivedController; 
  virtual int helper();
};

class DerivedController : public controller_interface::MultiInterfaceController<
    hardware_interface::VelocityJointInterface, hardware_interface::EffortJointInterface>
{
public:
  bool init(hardware_interface::RobotHW* robot_hw, ros::NodeHandle& root_nh, ros::NodeHandle& controller_nh);
  void update(const ros::Time&, const ros::Duration&);
  boost::scoped_ptr<ExtendingController> base_controller;
};

}  // namespace controller_manager_tests

#endif  // CONTROLLER_MANAGER_TESTS_EXTENSIBLE_CONTROLLERS_H