mozilla/rust — pull request #5328 by bstrie (2013-03-12 02:45:32+00:00)
Title: Implement Add on Option types

This will allow you to use the `+` operator to add together any two
Options, assuming that the contents of each Option likewise implement
`+`. So Some(4) + Some(1) == Some(5), and adding with None leaves the
other value unchanged.

This might be monoidic? I don't know what that word means!