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(
11 any(from_method = "from_error", from_method = "from_ok"),
12 from_desugaring = "QuestionMark"
14 message = "the `?` operator can only be used in {ItemContext} \
15 that returns `Result` or `Option` \
16 (or another type that implements `{Try}`)",
17 label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`",
18 enclosing_scope = "this function should return `Result` or `Option` to accept `?`"
21 all(from_method = "into_result", from_desugaring = "QuestionMark"),
22 message = "the `?` operator can only be applied to values \
23 that implement `{Try}`",
24 label = "the `?` operator cannot be applied to type `{Self}`"
29 /// The type of this value when viewed as successful.
30 #[unstable(feature = "try_trait", issue = "42327")]
32 /// The type of this value when viewed as failed.
33 #[unstable(feature = "try_trait", issue = "42327")]
36 /// Applies the "?" operator. A return of `Ok(t)` means that the
37 /// execution should continue normally, and the result of `?` is the
38 /// value `t`. A return of `Err(e)` means that execution should branch
39 /// to the innermost enclosing `catch`, or return from the function.
41 /// If an `Err(e)` result is returned, the value `e` will be "wrapped"
42 /// in the return type of the enclosing scope (which must itself implement
43 /// `Try`). Specifically, the value `X::from_error(From::from(e))`
44 /// is returned, where `X` is the return type of the enclosing function.
45 #[unstable(feature = "try_trait", issue = "42327")]
46 fn into_result(self) -> Result<Self::Ok, Self::Error>;
48 /// Wrap an error value to construct the composite result. For example,
49 /// `Result::Err(x)` and `Result::from_error(x)` are equivalent.
50 #[unstable(feature = "try_trait", issue = "42327")]
51 fn from_error(v: Self::Error) -> Self;
53 /// Wrap an OK value to construct the composite result. For example,
54 /// `Result::Ok(x)` and `Result::from_ok(x)` are equivalent.
55 #[unstable(feature = "try_trait", issue = "42327")]
56 fn from_ok(v: Self::Ok) -> Self;