[swift-users] "Unavailable instance method... used to satisfy a requirement of protocol"

[Jordan Rose]

Hi, James. The trick here is that the name you’ll get in Swift for these methods is probably 'compareQuery(_:toQuery:)', because the Swift compiler detects that the “result” is redundant with the type name. In Xcode 8 the compiler didn’t check if you were using the “old" name to satisfy a protocol, but Xcode 9 now does (for unrelated reasons).

Since this is a source-breaking change, can you file an issue at https://bugs.swift.org <https://bugs.swift.org/> ? At the very least we should make the diagnostic better.

You can always tell the Swift compiler you know better by using the NS_SWIFT_NAME annotation to provide an alternate name, using Swift function name syntax.

Jordan


> On Sep 15, 2017, at 12:45, James Dempsey via swift-users <swift-users at swift.org> wrote:
> 
> I am updating from Xcode 8 to Xcode 9, still using Swift 3.
> 
> In my project I am getting warnings of the pattern:
> 
> Unavailable instance method ‘compareQueryResult(_:toQueryResult:)’ was used to satisfy a requirement of protocol ‘ResultComparable’.
> 
> My project uses an Obj-C++ framework to wrap C++ and expose it in Obj-C.
> 
> The instance method in question is declared and implemented in a number of Obj-C classes in this framework.
> 
> @interface DocumentQuery: Query {
>    - (ComparisonResult)compareQueryResult:(DocumentResult *)result1 toQueryResult:(DocumentResult *)result2;
> }
> @end
> 
> @interface GroupQuery: Query {
>    - (ComparisonResult)compareQueryResult:(GroupResult *)result1 toQueryResult:(GroupResult *)result2;
> }
> @end
> 
> 
> 
> Another framework imports the Obj-C++ framework. In this framework the protocol is defined in Swift with an associated type:
> 
> public protocol ResultComparable
> {
>     associatedtype ResultType
>     func compareQueryResult(_ r1: ResultType, toQueryResult r2: ResultType) -> ComparisonResult
> }
> 
> And conformance is declared:
> 
> extension DocumentQuery: ResultComparable {}
> extension GroupQuery: ResultComparable {}
> 
> 
> This compiled without warnings in Xcode 8 / Swift 3, but they appear in Xcode 9 / Swift 3. Any help in understanding the issue and how to fix it would be greatly appreciated.
> 
> James
> 
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

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