The tracking issue for this feature is: #42327

This introduces a new trait Try for extending the ? operator to types other than Result (a part of RFC 1859). The trait provides the canonical way to view a type in terms of a success/failure dichotomy. This will allow ? to supplant the try_opt! macro on Option and the try_ready! macro on Poll, among other things.

Here's an example implementation of the trait:

/// A distinct type to represent the `None` value of an `Option`.
/// This enables using the `?` operator on `Option`; it's rarely useful alone.
#[unstable(feature = "try_trait", issue = "42327")]
pub struct None { _priv: () }

#[unstable(feature = "try_trait", issue = "42327")]
impl<T> ops::Try for Option<T>  {
    type Ok = T;
    type Error = None;

    fn into_result(self) -> Result<T, None> {
        self.ok_or(None { _priv: () })

    fn from_ok(v: T) -> Self {

    fn from_error(_: None) -> Self {

Note the Error associated type here is a new marker. The ? operator allows interconversion between different Try implementers only when the error type can be converted Into the error type of the enclosing function (or catch block). Having a distinct error type (as opposed to just (), or similar) restricts this to where it's semantically meaningful.