open class AsyncOperation: Operation {
  override open var isAsynchronous: Bool { return true }
}

public final class AsyncValueBlockOperation: AsyncOperation {
  public override var isAsynchronous: Bool { return false }
}

let _ = AsyncValueBlockOperation().isAsynchronous

2018-07-09 13:02:13.382072+0300 InheritanceProblem[25255:1883449] -[InheritanceProblem.AsyncValueBlockOperation asynchronous]: unrecognized selector sent to instance 0x102a06ff0

2018-07-09 13:02:13.385179+0300 InheritanceProblem[25255:1883449] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[InheritanceProblem.AsyncValueBlockOperation asynchronous]: unrecognized selector sent to instance 0x102a06ff0'

*** First throw call stack:
(
0   CoreFoundation                      0x00007fff5721132b __exceptionPreprocess + 171
1   libobjc.A.dylib                     0x00007fff7e367c76 objc_exception_throw + 48
2   CoreFoundation                      0x00007fff572a9e04 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3   CoreFoundation                      0x00007fff57187870 ___forwarding___ + 1456
4   CoreFoundation                      0x00007fff57187238 _CF_forwarding_prep_0 + 120
5   InheritanceProblem                  0x0000000100001c24 main + 52
6   libdyld.dylib                       0x00007fff7ef81015 start + 1
7   ???                                 0x0000000000000001 0x0 + 1
)

libc++abi.dylib: terminating with uncaught exception of type NSException

Program ended with exit code: 9