I feel like we’re talking past each other right now, so I’ll give a concrete
example:
Let’s say MyAwesomeFramework.framework defines this enum:
enum Access {
case none
case readOnly
case readWrite
}
This framework is compiled, built, and embedded in to
MyAwesomeApp.app/Frameworks.
Somewhere in MyAwesomeApp, I switch on the access of a thing:
switch aThing.access {
case .none: break
case .readOnly: print(“I can read”)
case .readWrite: print(“I can write”)
}
Let’s here observe some things:
1️⃣ the enum “Access” is *not* declared as frozen, because it might get a new
case in the future (such as “writeOnly”)
2️⃣ the switch on an Access value is exhaustive
3️⃣ under the proposal, I’m going to get a warning on the switch because Access
is not frozen. That warning will tell me to add “unknown case:”
This is the problem I’m talking about. The warning I’ll get on the switch is
technically correct (I’m switching on a non-frozen enum), but semantically
incorrect (it’s ok because the framework CANNOT introduce a new case without
recompilation of the switch statement, because they are packaged together). The
compiler will tell me to add an unknown case statement to the switch when it
will be completely unnecessary. Since MyAwesomeFramework.framework is embedded
in my app, there is no binary compatibility concern here, and I will never come
across an unknown case.
I think this false positive is going to be very common, because lots of people
embed frameworks in their apps, and those frameworks declare enums. Until the
frameworks are updated to freeze the enums, the app authors will be forced to
add “unknown case” statements to their switches for places where it is entirely
unnecessary. (This brings up the question: does this proposal include a fixit
to remove an “unknown case” statement from switches where it’s unnecessary?)
So, what I’m asking for is a part in the proposal (likely under “Future
Directions”) where you acknowledge this problem (the “false positive problem
for embedded modules”) and list it as something we’d like to solve in the
future.
Dave
> On Jan 12, 2018, at 4:27 PM, Dave DeLong via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>> On Jan 12, 2018, at 4:22 PM, Jordan Rose <jordan_r...@apple.com
>> <mailto:jordan_r...@apple.com>> wrote:
>>
>> No, it's "Revision-locked imports”.
>
> Ah, yeah I can see how the rev-locked imports is a variation on “I’ve copied
> in this library”.
>
>> A source-breaking change is one in which updating the library at compile
>> time will break clients at compile time. That's relevant for libraries
>> distributed with an app as well as for libraries that are part of the OS.
>> You may not care, but I do, and I think other package authors will too.
>
> ??? Of course I care about getting warnings when I’ve chosen to update a
> dependency. Where did I ever imply otherwise?
>
> What I’m saying is that if I’m embedding such a library in my app *now* and
> I’m importing it *now*, I shouldn’t get a warning about handling unknown
> cases off non-frozen enums *now*.
>
> And if I am going to see such warnings now, then the document needs to
> include how those “false positives” will be eliminated in the future.
>
> Dave
> _______________________________________________
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> swift-evolution@swift.org
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