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+# Extension of types used for command and state interfaces
+
+For introduction the file about general [purpose inputs/outputs in ros2_control](non_joint_command_interfaces.md).
+
+## Motivation
+Many GPIO values used in modern robots are logical and not numeric values.
+For example, a vacuum valve at the robot has "on" (true) and "off" (false) states.
+
+## Problem
+Currently, the `ros2_control` framework supports only the `double` type to exchange data between hardware and controllers.
+This is confusing for users and it would be clearer if also boolean and integer values can be transported.
+
+## Possible solution
+Extend [`ReadOnlyHandle`](https://github.com/ros-controls/ros2_control/blob/93b15787f1d2e16dd41d202cebff5fdbef56e19d/hardware_interface/include/hardware_interface/handle.hpp#L31) to accept other primitive types like `bool`, `int`, and unsigned types.
+This could be simply done by templating the class, or to keep it restricted implementing constructors, getters and setters for those types.
+The latter could become complex to keep track about specific types.