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Selector: Message Selectors

interface Selector
{
  Message select(MessageQueue queue);
}

A selector returns the next message to be delivered from a channel from the queue of messages stored in the channel; it also updates the queue.

The default selector returns the oldest message in a channel (i.e., the message which was sent first); it is an object of type

class SelectorDefault implements Selector
{
  Message select(MessageQueue queue)
  {
    return queue.dequeue();
  }
}

The default selector may be redefined to implement different kind of channel failure modes (lost messages, duplicated messages, ...).