So it's a specialized mapping operator for the Result functor. Why restrict it to Result only? What about using option to denote a failure condition without a specific reason? Or other kinds of interesting functors?
> What about using option to denote a failure condition without a specific reason?
Result is set up and marked to mandate its use, the compiler will complain if you ignore the result of a function returning a Result, not so for an Option. So idiomatically denoting a failure condition without a specific reason is Result<T, ()> not Option<T>: http://doc.rust-lang.org/std/result/#result-and-option.
Option<T> is for what it's name denotes, a value which may or may not be present (e.g. an optional field in a struct).
To elaborate on this slightly, it's not that Result is special cased by the compiler, there's a 'must_use' attribute which ensures that you get a warning if you ignore it, and the definition of Result has it.
