Swift doesn't convert Objective-C NSError** to throws

Question

I have some Objective-C legacy code, that declares method like

- (void)doSomethingWithArgument:(ArgType)argument error:(NSError **)error

As

Answer 1

You need to make your method return a BOOL, to tell the runtime that an error should or should not be thrown. Also you should add __autoreleasing to the error parameter, to make sure ARC doesn't accidentally release the error before you have a chance to use it:

- (BOOL)doSomethingWithArgument:(ArgType)argument error:(NSError * __autoreleasing *)error

You can then call it from Swift like this:

do {
    object.doSomethingWithArgument(someArgument)
} catch let err as NSError {
    print("Error: \(err)")
}