Creating a new command

Introduction

Command (dynamicgraph::command::Command) are objects that encapsulate an action to be performed on an entity.

In this page, we define a new command that will call method InvertedPendulum::incr. The source code is in src/command-increment.hh.

Implementation

We first define the new class by deriving dynamicgraph::command::Command:

namespace dynamicgraph {
  namespace tutorial {
    namespace command {
      class Increment : public Command
      {

The constructor takes

• a reference to a InvertedPendulum and calls parent class,
• a vector a types specifying the number and types of input arguments of the command and
• a string documenting the command. In this case, there is only one argument of type double. Note the use of boost::assign::list_of to build a vector in one command line:

  Increment(InvertedPendulum& entity, const std::string& docstring) :
  Command(entity, boost::assign::list_of(Value::DOUBLE), docstring)
          {
          }

We then define the action of the command in virtual method doExecute. We need to get a reference to the object on which the command will act. Note that we can straightfowardly statically cast in InvertedPendulum the Entity object returned by method owner:

virtual Value doExecute()
{
  Entity& entity = owner();
  InvertedPendulum& ip = static_cast<InvertedPendulum&>(entity);

We then get the parameters as a vector of dynamicgraph::command::Value objects and cast them into the appropriate types specified at construction:

std::vector<Value> values = getParameterValues();
double timeStep = values[0].value();

Finally, we execute the action and return a value of the appropriate type, here the command return no value:

  ip.incr(timeStep);
  return Value();
}