class_loader

The class_loader package is a ROS-independent package for loading plugins during runtime and the foundation of the higher level ROS pluginlib library. class_loader utilizes the host operating system’s runtime loader to open runtime libraries (e.g. .so/.dll/dylib files), introspect the library for exported plugin classes, and allows users to instantiate objects of said exported classes without the explicit declaration (i.e. header file) for those classes.

class_loader VS pluginlib

class_loader is used in the implementation of the higher-level ROS package pluginlib which is the encouraged method for loading plugins in the ROS ecosystem. You should use class_loader when creating plugins intended for non-ROS packages and pluginlib when exporting plugins to ROS packages.

Quality Declaration

This package claims to be in the Quality Level 1 category, see the Quality Declaration for more details.

Usage

The interface is provided through two classes, class_loader::ClassLoader and class_loader::MultiLibraryClassLoader. Both provide similar interfaces but the former only binds to a single runtime library whereas the latter can associate with multiple libraries. The typical workflow is as follows:

  • Include class_loader/class_loader.h in your source code

  • Instantiate a class_loader::ClassLoader object passing the path and name of the library to open 

    class_loader::ClassLoader loader("libMyLibrary.so");

  • Query the class for exported classes which have an interface defined by some base class (MyBase in the example) 

    std::vector<std::string> classes = loader.getAvailableClasses<MyBase>()

  • Create/destroy objects of said exported classes 

    for(unsigned int c = 0; c < classes.size(); ++c)
{
  boost::shared_ptr<MyBase> plugin = loader.createInstance<MyBase>(classes[c]);
  plugin->someMethod();
  //'plugin' will automatically be deleted when it goes out of scope
}

  • Destroy the ClassLoader object to shutdown the library.

Example: Basic Workflow for ClassLoader

#include <class_loader/class_loader.h>
#include "MyBase.h" //Defines class MyBase

int main()
{
  class_loader::ClassLoader loader("libMyLibrary.so");
  std::vector<std::string> classes = loader.getAvailableClasses<MyBase>();
  for(unsigned int c = 0; c < classes.size(); ++c)
  {
    boost::shared_ptr<MyBase> plugin = loader.createInstance<MyBase>(classes[c]);
    plugin->someMethod();
  }
}

Visit the class_loader API documentation for a complete list of its main components.

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