Converting to Swift 3 renamed my own Objective-C m

Question

I have swift classes mixed in with my Objective-C code. With Swift 2.3, everything was fine and worked as expected.

I recently converted to Swift 3, and it updates several API calls because of all the renaming that occurred for Swift 3. That's fine; I get that.

But what's not fine is that Swift 3 seems to have renamed a method in one of my Objective-C classes. I own the Objective-C class and I called the method what I wanted: readDeliveryInfoItems. But now, after converting to Swift 3, I can't call .readDeliveryInfoItems() anymore in my Swift class. It's telling me it has been renamed to .readItems().

That makes no sense. And the Objective-C class still calls the method readDeliveryInfoItems, so there is something under the covers going on here.

I have tried renaming the Objective-C readDeliveryInfoItems method to readDeliveryInfo, building (Swift fails because it says that the readInfo() method doesn't exist, which is good), and then renaming the method back to readDeliveryInfoItems. However, when I build after this, Swift goes back to thinking the method is called readInfo(). I was hoping this would trick Xcode into refreshing the Swift bridging and renaming the method back to the correct name readDeliveryInfoItems(), but it did not.

How can I fix this?

UPDATE TO ADD MORE INFO

The interface of my Objective-C class has this function declaration:

- (nullable NSArray<XMPPDeliveryInfoItem *> *)readDeliveryInfoItems;

But in the Generated Interface (see MartinR's comment below) for that class, the function declaration is this instead:

open func readItems() -> [XMPPDeliveryInfoItem]?

There are other functions in that class that are similar to the readDeliveryInfoItems function, such as this one:

- (nullable NSArray<XMPPDeliveryInfoItem *> *)sentDeliveryInfoItems;

And they look correct in the Generated Interface:

open func sentDeliveryInfoItems() -> [XMPPDeliveryInfoItem]?

So I can't figure out why I'm having this problem with only the one function.

Answer 1

Roughly speaking (and I am oversimplifying), if the suffix on a method name is a verb object matching the return type, the suffix is dropped.

A simpler example would be a method called readString that returns an NSString.

Your method falls within those parameters (I told you I was oversimplifying but you can see, roughly, how that's true), so you get the treatment.

Personally, I regard this as a bug, especially because in some cases the change can result in name clash and make calling the method impossible (esp. when the Objective-C API is not yours and you cannot change it). For an example, see this question: Swift 3 (Omit Needless Words) causing two functions to have the same name

Answer 2

The translation process is described in detail in

• SE-0005 Better Translation of Objective-C APIs Into Swift

The relevant part for your question is (emphasis mine):

Prune a match for the enclosing type from the base name of a method so long as the match starts after a verb. For example,

extension UIViewController {
  func dismissViewControllerAnimated(flag: Bool, completion: (() -> Void)? = nil)
}

becomes:

extension UIViewController {
  func dismissAnimated(flag: Bool, completion: (() -> Void)? = nil)
}

This pruning algorithm is – as far as I can see – implemented in StringExtras.cpp (and uses a lot of heuristics), and PartsOfSpeech.def contains a list of words which are considered a verb, such as

VERB(dismiss)
VERB(read)
VERB(send)

but not VERB(sent). That explains why – simplifying your example slightly –

@interface DeliveryInfo : NSObject
-(void)readDeliveryInfoItems;
-(void)sentDeliveryInfoItems;
@end

becomes

open class DeliveryInfo : NSObject {
    open func readItems()
    open func sentDeliveryInfoItems()
}

The type name is pruned after the verb "read", but not after the non-verb "sent". (You can verify that by changing the second method name to sendDeliveryInfoItems which is then mapped to sendItems().)

You can override the mapping with NS_SWIFT_NAME:

-(void)readDeliveryInfoItems NS_SWIFT_NAME(readDeliveryInfoItems());