[swift-evolution] [swift-evolution-announce] [Review] SE 0192 - Non-Exhaustive Enums

Goffredo Marocchi panajev at gmail.com
Fri Jan 5 02:14:51 CST 2018

Code that ends up running in a default case somewhere in one of the several places you switch over that enum that you forgot about... well, it may not break source code compatibility, but it may introduce subtle bugs... submarine bugs.

Sent from my iPhone

> On 5 Jan 2018, at 08:11, Goffredo Marocchi via swift-evolution <swift-evolution at swift.org> wrote:
>> On 5 Jan 2018, at 00:38, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
>> Furthermore, the old code needs to continue working without source changes, because updating to a new SDK must not break existing code. (It can introduce new warnings, but even that is something that should be considered carefully.)
>> So: this proposal is designed to handle the use cases both for Swift library authors to come and for C APIs today, and in particular Apple's Objective-C SDKs and how they've evolved historically.
> I will let your very comprehensive rationale brew a little bit more in my mind and reread it, but I still think this is a bit leaning too much over to library authors than library consumers (not unlike the closed by default discussion we all had a while ago).
> I remain very unconvinced by the “updating library/SDK” must be source compatible. Especially if it is major version change and a deprecated method has been removed, methods have changed signature, etc... Backward compatible runtime with code compiled against the previous SDK yes, source compatible no.
> I feel like this change will make the life easier for library authors, but risks making it easier and easier to make mistakes in apps using the libraries: exhaustive switching over enums is a good important feature that risks going away (the default matters) for not a huge effective benefit to app developers.
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