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| // Copyright 2012 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| /// This trait has been superseded by the `Try` trait, but must remain | ||
| /// here as `?` is still lowered to it in stage0 . | ||
| #[cfg(stage0)] | ||
| #[unstable(feature = "question_mark_carrier", issue = "31436")] | ||
| pub trait Carrier { | ||
| /// The type of the value when computation succeeds. | ||
| type Success; | ||
| /// The type of the value when computation errors out. | ||
| type Error; | ||
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| /// Create a `Carrier` from a success value. | ||
| fn from_success(_: Self::Success) -> Self; | ||
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| /// Create a `Carrier` from an error value. | ||
| fn from_error(_: Self::Error) -> Self; | ||
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| /// Translate this `Carrier` to another implementation of `Carrier` with the | ||
| /// same associated types. | ||
| fn translate<T>(self) -> T where T: Carrier<Success=Self::Success, Error=Self::Error>; | ||
| } | ||
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| #[cfg(stage0)] | ||
| #[unstable(feature = "question_mark_carrier", issue = "31436")] | ||
| impl<U, V> Carrier for Result<U, V> { | ||
| type Success = U; | ||
| type Error = V; | ||
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| fn from_success(u: U) -> Result<U, V> { | ||
| Ok(u) | ||
| } | ||
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| fn from_error(e: V) -> Result<U, V> { | ||
| Err(e) | ||
| } | ||
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| fn translate<T>(self) -> T | ||
| where T: Carrier<Success=U, Error=V> | ||
| { | ||
| match self { | ||
| Ok(u) => T::from_success(u), | ||
| Err(e) => T::from_error(e), | ||
| } | ||
| } | ||
| } | ||
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| struct _DummyErrorType; | ||
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| impl Try for _DummyErrorType { | ||
| type Ok = (); | ||
| type Error = (); | ||
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| fn into_result(self) -> Result<Self::Ok, Self::Error> { | ||
| Ok(()) | ||
| } | ||
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| fn from_ok(_: ()) -> _DummyErrorType { | ||
| _DummyErrorType | ||
| } | ||
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| fn from_error(_: ()) -> _DummyErrorType { | ||
| _DummyErrorType | ||
| } | ||
| } | ||
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| /// A trait for customizing the behaviour 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")] | ||
| 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; | ||
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| /// 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>; | ||
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| /// 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; | ||
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| /// 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; | ||
| } |