[swift-evolution] [Pitch] Typed throws

[Matthew Johnson]

> On Feb 17, 2017, at 1:42 PM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
> 
> So the typed throws are going to be limited to a single error type, is that the direction we're heading to?

Yes, this topic was discussed thoroughly last year.

> 
> -- 
> Adrian Zubarev
> Sent with Airmail
> 
> Am 17. Februar 2017 um 20:39:12, Anton Zhilin (antonyzhilin at gmail.com <mailto:antonyzhilin at gmail.com>) schrieb:
> 
>> In this case, you’d better create a new error type, which includes all the cases of those errors:
>> 
>> // FileNotFoundError and WrongFormat are Error-s
>> 
>> struct PreferencesError : Error {
>>     init(_: FileNotFoundError)
>>     init(_: WrongFormat)
>>     // ...
>> }
>> 
>> func readPreferences() throws(PreferencesError)
>> In the most “lazy” case, you’d just create an enum of those two:
>> 
>> enum PreferencesError : Error {
>>     case fileNotFound(FileNotFoundError)
>>     case wrongFormat(WrongFormatError)
>> }
>> Better yet, you should analyze, which cases are meaningful for user of 
>> readPreferences, and present them with appropriate interface. You may want to crash on those cases of initial error types, with which you can’t do anything on the level of abstraction of 
>> readPreferences. Some of the others will be merged or renamed.
>> 
>> With proper error types, a single type in 
>> throws clause is enough, without sum types.
>> 
>> 2017-02-17 22:22 GMT+03:00 Adrian Zubarev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>:
>> 
>> 
>> Sure thing, but that’s not what I was asking about. Kevin made a protocol that conforms to Error where all the his enums conformed to MyError protocol. That way we’re losing all enum cases and are not really a step further as before.
>> 
>> 
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