On balance I think I prefer result types. Java's fully typed throws and Swift's semi-typed throws are fine though. I can't see Swift supporting result types because they already have throws.
-- Howard. > On 6 Jul 2017, at 4:27 pm, Tim Wang <shenghai.w...@bigtincan.com> wrote: > > Thanks Howard, it's a good workaround. > > Do you think it would be better to be part of swift language feature? I wish > swift team could consider this :) > >> On Thu, Jul 6, 2017 at 11:04 AM Howard Lovatt <howard.lov...@gmail.com> >> wrote: >> You could use a result type, e.g.: >> >> https://github.com/antitypical/Result >> >> Or roll your own result type. >> >> I think the reason that Swift doesn't support what you want is because of >> rethrows. When you declare a method as rethrows it can throw anything >> because the closure it is re-throwing can throw anything. They could have >> fully typed the rethrows but obviously decided that was not worth it. At >> present rethrows is light weight; the compiler generates two versions of the >> method, one that throws and one that doesn't. If it was typed then it would >> be like a generic method and a version of the method would be required for >> each type combination that was actually used. >> >> -- Howard. >> >>> On 6 July 2017 at 10:38, Tim Wang via swift-users <swift-users@swift.org> >>> wrote: >> >>> Hi Swifters, >>> >>> I am wondering if it is possible to specify error types thrown in a >>> protocol method. By allowing us to do it and letting the compiler check all >>> the implementations of the protocol to make sure only they would only throw >>> the specified error types, we only need to catch our error types when >>> calling these methods. >>> >>> For the code below: >>> >>> enum MyError: Error { >>> >>> case justError >>> >>> } >>> >>> protocol MethodWillThrow { >>> >>> func testMethod() throws MyError >>> >>> } >>> >>> >>> >>> extension MethodThrow { >>> >>> func testMethod() throws { >>> >>> throw MyError.justError >>> >>> } >>> >>> } >>> >>> class TestClass: MethodThrow { >>> >>> func testMethod() throws { >>> >>> throw MyError.justError >>> >>> } >>> >>> func anotherMethod() { >>> >>> do { >>> >>> try testMethod() >>> >>> } catch MyError.justError { >>> >>> print("my error") >>> >>> } catch { >>> >>> print("other error") >>> >>> } >>> >>> } >>> >>> } >>> >>> Now we need add this extra default catch to make it compile and work and I >>> really want to remove this catch. >>> >>> Please let me know if there is a way to do it and thanks for help in >>> advance. >>> >>> Tim Wang >>> >>> >> >>> _______________________________________________ >>> swift-users mailing list >>> swift-users@swift.org >>> https://lists.swift.org/mailman/listinfo/swift-users >>>
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