PHP Manual: The setCallback purpose

Description

public void EventListener::setCallback( callable $cb , mixed $arg = null )

Adjust event connect listener's callback and optionally the callback argument.

Parameters

cb

The new callback for new connections. Ignored if null.

Should match the following prototype:

void callback(
     EventListener $listener = null ,
     mixed $fd = null ,
     array $address = null ,
     mixed $arg = null
)

listener: The EventListener object.
fd: The file descriptor or a resource associated with the listener.
address: Array of two elements: IP address and the server port.
arg: User custom data attached to the callback.

arg

Custom user data attached to the callback. Ignored if null.

Return Values

No value is returned.