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Error and .unwrap() do not agree on traits #21790

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maurer opened this issue Jan 30, 2015 · 4 comments · Fixed by #23541
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Error and .unwrap() do not agree on traits #21790

maurer opened this issue Jan 30, 2015 · 4 comments · Fixed by #23541
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@aturon
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I-needs-decision Issue: In need of a decision.
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1.0 beta

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@maurer
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maurer commented Jan 30, 2015

Error currently requires Display, while .unwrap() requires Debug.

I'm unsure of what each should require, but I think they should agree so that it is possible to have code which returns Result<_, Box<Error>> (which is useful to allow try! across functions returning different types of error codes), and be able to .unwrap() the results.
@Stebalien
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There was a lengthy discussion about this towards the bottom of the RFC: rust-lang/rfcs#565.

@steveklabnik
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/cc @aturon , I vaguely remember this might change? If not, then this should be in the RFCs repo.

@aturon
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aturon commented Feb 16, 2015

Nominating for 1.0-beta P-backcompat-libs.

(The Error trait isn't #[stable] yet, but it probably will be for 1.0).

@pnkfelix
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1.0 beta, P-backcompat-libs, I-needs-decision.

@pnkfelix pnkfelix added I-needs-decision Issue: In need of a decision. P-backcompat-libs labels Feb 19, 2015
@pnkfelix pnkfelix added this to the 1.0 beta milestone Feb 19, 2015
@aturon aturon mentioned this issue Mar 20, 2015
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alexcrichton added a commit to alexcrichton/rust that referenced this issue Mar 23, 2015
@alexcrichton
rollup merge of rust-lang#23541: aturon/stab-error
b97e1cc 
This small commit stabilizes the `Error` trait as-is, except that `Send`
and `Debug` are added as constraints. The `Send` constraint is because
most uses of `Error` will be for trait objects, and by default we would
like these objects to be transferrable between threads. The `Debug`
constraint is to ensure that e.g. `Box<Error>` is `Debug`, and because
types that implement `Display` should certainly implement `Debug` in any case.

In the near future we expect to add `Any`-like downcasting features to
`Error`, but this is waiting on some additional
mechanisms (`Reflect`). It will be added before 1.0 via default methods.

[breaking-change]

r? @alexcrichton

Closes rust-lang#21790
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@aturon aturon

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Stabilize the Error trait aturon/rust
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@steveklabnik @maurer @pnkfelix @Stebalien @kmcallister @aturon