SendPorts are created from ReceivePorts. Any message sent through a SendPort is delivered to its respective ReceivePort. There might be many SendPorts for the same ReceivePort.

SendPorts can be transmitted to other isolates.

abstract class SendPort {

  /**
   * Sends an asynchronous [message] to this send port. The message is copied to
   * the receiving isolate. If specified, the [replyTo] port will be provided to
   * the receiver to facilitate exchanging sequences of messages.
   *
   * The content of [message] can be: primitive values (null, num, bool, double,
   * String), instances of [SendPort], and lists and maps whose elements are any
   * of these. List and maps are also allowed to be cyclic.
   *
   * In the special circumstances when two isolates share the same code and are
   * running in the same process (e.g. isolates created via [spawnFunction]), it
   * is also possible to send object instances (which would be copied in the
   * process). This is currently only supported by the dartvm.  For now, the
   * dart2js compiler only supports the restricted messages described above.
   *
   * Deprecation note: it is no longer valid to transmit a [ReceivePort] in a
   * message. Previously they were translated to the corresponding send port
   * before being transmitted.
   */
  void send(var message, [SendPort replyTo]);

  /**
   * Sends a message to this send port and returns a [Future] of the reply.
   * Basically, this internally creates a new receive port, sends a
   * message to this send port with replyTo set to such receive port, and, when
   * a reply is received, it closes the receive port and completes the returned
   * future.
   */
  Future call(var message);

  /**
   * Tests whether [other] is a [SendPort] pointing to the same
   * [ReceivePort] as this one.
   */
  bool operator==(var other);

  /**
   * Returns an immutable hash code for this send port that is
   * consistent with the == operator.
   */
  int get hashCode;

}