It only supports eventual sends, with only a fail-stop guarantee, rather than guaranteed delivery. Once it fails, it will never again deliver any messages, and it will eventually become Broken . A Broken reference is strictly weaker than Eventual or Near references. It does not and never will designate an object. Instead, it holds a Throwable to indicate what problem caused it not to designate an object.
Broken references are transitively immutable and are transitively passed by copy.
Vertical Taxonomy A reference is either a Promise or Resolved . Messages sent to an Promise are queued, awaiting the Promise's resolution. Should the Promise become fulfilled, whether to a Near or Far reference, these messages will be delivered to that object. The result of an eventual-send always starts as a Promise for the outcome. Promises are Unsettled.