> On Feb 24, 2017, at 11:00 AM, Joe Groff via swift-evolution > <swift-evolution@swift.org> wrote: > > >> On Feb 23, 2017, at 10:36 PM, Russ Bishop <xen...@gmail.com >> <mailto:xen...@gmail.com>> wrote: >> >> >>> On Feb 21, 2017, at 8:18 AM, Joe Groff <jgr...@apple.com >>> <mailto:jgr...@apple.com>> wrote: >>>>> >>>> >>>> Yeah but Rust has a macro system so error-chain makes re-wrapping trivial. >>>> A simple `chain_err(|| “my new error message”)` is enough to define and >>>> “throw” a new error that wraps the underlying error. >>> >>> That was my point—they recognized error chaining/layering as a common >>> phonemenon and provided affordances for it as part of their design. I was >>> saying we should do the same if we investigate typed errors seriously. (Not >>> sure why you mentioned macros—chain_err is just a regular method, and could >>> be defined as an extension method on Error in swift today.) >>> >>> -Joe >> >> Sorry, I meant error_chain! handles the boilerplate. At the end of the day >> something has to create the new error types. >> >> I agree with you on the chaining; if we really do want to go down this road >> we need an elegant solution. Seeing people talk about getting rid of >> rethrows makes me think this isn’t yet a serious discussion.
Is it just the syntactic sugar you would miss or is there more to it? Did you see the analysis I sent out showing a case rethrows can’t handle and a problem the current proposal has in handling typed rethrows? > > If `rethrows` can be turned into sugar for regular type parametricity, I > think that'd be a win over our current model. The sugar is probably still > useful since `<E> (() throws E -> ()) throws SomethingDerivedFrom<E> -> ()` > is common enough; whether SomethingDerivedFrom<E> is E, Error, or > MyModulesErrorWrapper<E> would have to be discussed. I don’t mind keeping rethrows as syntactic sugar but I would like to have a solution that can handle all cases including the one it isn’t able to handle. I almost included something like this in the analysis I sent out. I thought maybe injecting implicit generic parameters would be a little bit too magical. It would be super convenient though! > > -Joe > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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