| /// A trait for customizing the behavior of the `?` operator. |
| /// |
| /// A type implementing `Try` is one that has a canonical way to view it |
| /// in terms of a success/failure dichotomy. This trait allows both |
| /// extracting those success or failure values from an existing instance and |
| /// creating a new instance from a success or failure value. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| #[rustc_on_unimplemented( |
| on( |
| all( |
| any(from_method = "from_error", from_method = "from_ok"), |
| from_desugaring = "QuestionMark" |
| ), |
| message = "the `?` operator can only be used in {ItemContext} \ |
| that returns `Result` or `Option` \ |
| (or another type that implements `{Try}`)", |
| label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`", |
| enclosing_scope = "this function should return `Result` or `Option` to accept `?`" |
| ), |
| on( |
| all(from_method = "into_result", from_desugaring = "QuestionMark"), |
| message = "the `?` operator can only be applied to values \ |
| that implement `{Try}`", |
| label = "the `?` operator cannot be applied to type `{Self}`" |
| ) |
| )] |
| #[doc(alias = "?")] |
| pub trait Try { |
| /// The type of this value when viewed as successful. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| type Ok; |
| /// The type of this value when viewed as failed. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| type Error; |
| |
| /// Applies the "?" operator. A return of `Ok(t)` means that the |
| /// execution should continue normally, and the result of `?` is the |
| /// value `t`. A return of `Err(e)` means that execution should branch |
| /// to the innermost enclosing `catch`, or return from the function. |
| /// |
| /// If an `Err(e)` result is returned, the value `e` will be "wrapped" |
| /// in the return type of the enclosing scope (which must itself implement |
| /// `Try`). Specifically, the value `X::from_error(From::from(e))` |
| /// is returned, where `X` is the return type of the enclosing function. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| fn into_result(self) -> Result<Self::Ok, Self::Error>; |
| |
| /// Wrap an error value to construct the composite result. For example, |
| /// `Result::Err(x)` and `Result::from_error(x)` are equivalent. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| fn from_error(v: Self::Error) -> Self; |
| |
| /// Wrap an OK value to construct the composite result. For example, |
| /// `Result::Ok(x)` and `Result::from_ok(x)` are equivalent. |
| #[unstable(feature = "try_trait", issue = "42327")] |
| fn from_ok(v: Self::Ok) -> Self; |
| } |