1 /// A trait for customizing the behavior of the `?` operator.
3 /// A type implementing `Try` is one that has a canonical way to view it
4 /// in terms of a success/failure dichotomy. This trait allows both
5 /// extracting those success or failure values from an existing instance and
6 /// creating a new instance from a success or failure value.
7 #[unstable(feature = "try_trait", issue = "42327")]
8 #[rustc_on_unimplemented(
10 any(from_method="from_error", from_method="from_ok"),
12 message="the `?` operator can only be used in a \
13 function that returns `Result` or `Option` \
14 (or another type that implements `{Try}`)",
15 label="cannot use the `?` operator in a function that returns `{Self}`"),
16 on(all(from_method="into_result", from_desugaring="?"),
17 message="the `?` operator can only be applied to values \
18 that implement `{Try}`",
19 label="the `?` operator cannot be applied to type `{Self}`")
23 /// The type of this value when viewed as successful.
24 #[unstable(feature = "try_trait", issue = "42327")]
26 /// The type of this value when viewed as failed.
27 #[unstable(feature = "try_trait", issue = "42327")]
30 /// Applies the "?" operator. A return of `Ok(t)` means that the
31 /// execution should continue normally, and the result of `?` is the
32 /// value `t`. A return of `Err(e)` means that execution should branch
33 /// to the innermost enclosing `catch`, or return from the function.
35 /// If an `Err(e)` result is returned, the value `e` will be "wrapped"
36 /// in the return type of the enclosing scope (which must itself implement
37 /// `Try`). Specifically, the value `X::from_error(From::from(e))`
38 /// is returned, where `X` is the return type of the enclosing function.
39 #[unstable(feature = "try_trait", issue = "42327")]
40 fn into_result(self) -> Result<Self::Ok, Self::Error>;
42 /// Wrap an error value to construct the composite result. For example,
43 /// `Result::Err(x)` and `Result::from_error(x)` are equivalent.
44 #[unstable(feature = "try_trait", issue = "42327")]
45 fn from_error(v: Self::Error) -> Self;
47 /// Wrap an OK value to construct the composite result. For example,
48 /// `Result::Ok(x)` and `Result::from_ok(x)` are equivalent.
49 #[unstable(feature = "try_trait", issue = "42327")]
50 fn from_ok(v: Self::Ok) -> Self;