Adding existing Tasks into containers to create more complex tasks

[robotics-qc]

Hello!

I am curious to know if there is a way to add a Task into a container - so for example if we have a dual arm setup, and have pipelines for pick and place for each one -

Is there an easy way for me to create an alternatives container and just add two existing task pipelines into it/ extract the stages into a container to pass on to the alternatives block?

For example:
Provided I have functions that return task objects - is there a way to do something like this

    moveit::task_constructor::Task pickObjectEitherHandTask(std::string object)
    {
        // Initialize the task
        moveit::task_constructor::Task task;
        task.setName("pick object with both hands: " + object);

        // Load robot model
        task.loadRobotModel(shared_from_this());
        initialize_planners();

        // Create Alternatives stage to evaluate both arms
        auto alternatives = std::make_unique<moveit::task_constructor::Alternatives>("pick with left or right arm");

        // Add left arm task

        auto left_arm_task = pickObjectLeftTask(object);

        alternatives->add(std::move(left_arm_task.stages()));

        // Add right arm task

        auto right_arm_task = pickObjectRightTask(object);

        alternatives->add(std::move(right_arm_task.stages()));

        // Add Alternatives stage to the main task
        task.add(std::move(alternatives));

        return task;
    }

[rhaschke]

No, that's not possible. This would require to move the stage from an existing task/container into another one, which is not supported as this would invalidate the original task. The stages() method just returns a raw pointer for access.
The solution is to have the pickObjectLeft|Right functions return a container unique pointer instead of a task.