This interface provides the means to bypass such features, thus improving performance. The state is an arbitrary object, the meaning of which is determined by the operations. The operations are defined by a mapping from names to procedures. Applications can assume that the standard input operations are implemented for all input ports, and likewise the standard output operations are implemented for all output ports.
Some ports support additional operations.
Because only some ports will implement these operations, programs that use custom operations must test each port for their existence, and be prepared to deal with ports that do not implement them.