但在 Xcode 10.3 中失败，但在 Xcode 11.3 中工作

Question

I have a piece of code that builds without a problem in Xcode 11.3 but fails in Xcode 10.3. I think that's because Xcode 10.3 doesn't have the required compiler. The code implements push notifications that don't work in Xcode 11.3 but work in Xcode 10.3 (something to do with this - that's why I want to build in Xcode 10.3). Is there anything I can do to build in Xcode 10.3?

Update with code:

func signalRecipients(transaction: SDSAnyReadTransaction) -> [SignalRecipient] {
    e164sForIntersection.compactMap { e164Number in
        let address = SignalServiceAddress(phoneNumber: e164Number)
        return SignalRecipient.registeredRecipient(for: address, mustHaveDevices: true, transaction: transaction)
    }
}

In Xcode 11.3 no errors. In Xcode 10.3: "Unable to infer complex closure return type; add explicit type to disambiguate"

    var hasViewed: Bool { firstViewedTimestamp > 0 }

In Xcode 11.3 no errors. In Xcode 10.3: "Missing return in a function expected to return 'Bool'".

I think the behavior is due to the compiler from Xcode 10.3. Could I somehow use the compiler from Xcode 11.3 to Xcode 10.3?

Answer 1

The error messages tell you what you need to know.

• The first one is an expression that is too complex for type interference for 10.3, so give it some types. Like e164Number in -> whatever type.

• The second one tells you clearly that you are not returning a bool expression. Looking at the code, true, there is no return statement. So add a return statement.

Answer 2

I think the behavior is due to the compiler from Xcode 10.3.

Of course it does.

Could I somehow use the compiler from Xcode 11.3 to Xcode 10.3?

No: what you do is write code that works with both compilers.

Let's be clearer. This has to do only indirectly with the version of Xcode. What's really important is the version of Swift . Different versions of Swift have different compilers and different language rules, as the language evolves over time.

Let's take the second one:

var hasViewed: Bool { firstViewedTimestamp > 0 }

In Xcode 11.3 no errors. In Xcode 10.3: "Missing return in a function expected to return 'Bool'".

Correct. In Swift 5.1 a new rule was introduced that it is legal to omit the keyword return in a one-line function body. But the rule is new, so for an earlier version of Swift you still have to say that the old way:

var hasViewed: Bool { return firstViewedTimestamp > 0 }

That will work for both older and newer versions of Swift, so just use that and all will be well.