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3b2f2976 | 1 | /// A trait for customizing the behavior of the `?` operator. |
041b39d2 XL |
2 | /// |
3 | /// A type implementing `Try` is one that has a canonical way to view it | |
9fa01778 | 4 | /// in terms of a success/failure dichotomy. This trait allows both |
041b39d2 XL |
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")] | |
60c5eb7d XL |
8 | #[cfg_attr( |
9 | not(bootstrap), | |
10 | rustc_on_unimplemented( | |
11 | on( | |
12 | all( | |
13 | any(from_method = "from_error", from_method = "from_ok"), | |
14 | from_desugaring = "QuestionMark" | |
15 | ), | |
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 `?`" | |
21 | ), | |
22 | on( | |
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}`" | |
27 | ) | |
28 | ) | |
29 | )] | |
83c7162d | 30 | #[doc(alias = "?")] |
041b39d2 XL |
31 | pub trait Try { |
32 | /// The type of this value when viewed as successful. | |
33 | #[unstable(feature = "try_trait", issue = "42327")] | |
34 | type Ok; | |
35 | /// The type of this value when viewed as failed. | |
36 | #[unstable(feature = "try_trait", issue = "42327")] | |
37 | type Error; | |
38 | ||
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. | |
43 | /// | |
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>; | |
50 | ||
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; | |
55 | ||
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; | |
60 | } |