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