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