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# 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](./QUALITY_DECLARATION.md) 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](https://wiki.ros.org/class_loader) API documentation for a complete list of its main components.
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