As of Xcode 10.2, when using enums I've defined in Objective-C, but in a Swift 5 switch statement, I get the following warning, even if I've exhausted all the possible enum values.
Switch covers known cases, but 'MyObjectiveCEnumName' may have additional
unknown values
Xcode is telling me I should fix this by
Handle unknown values using "@unknown default"
Why is this happening and what can I do about it?
Objective-C enum
typedef NS_ENUM(NSUInteger, CardColor) {
CardColorBlack,
CardColorRed
};
Swift 5 switch statement
var cardColor: CardColor = .black
switch (cardColor) {
case .black:
print("black")
case .red:
print("red")
}
If you want Objective-C enums to be treated just like Swift ones, you now need to declare them using a different macro, NS_CLOSED_ENUM, versus the old NS_ENUM. Changing this will make the warning disappear.
The example above would become
typedef NS_CLOSED_ENUM(NSUInteger, CardColor) {
CardColorBlack,
CardColorRed
};
From the Swift 5 release notes:
In Swift 5 mode, switches over enumerations that are declared in Objective-C or that come from system frameworks are required to handle unknown cases—cases that might be added in the future, or that may be defined privately in an Objective-C implementation file. Formally, Objective-C allows storing any value in an enumeration as long as it fits in the underlying type. These unknown cases can be handled by using the new @unknown default case, which still provides warnings if any known cases are omitted from the switch. They can also be handled using a normal default case.
If you’ve defined your own enumeration in Objective-C and you don’t need clients to handle unknown cases, you can use the NS_CLOSED_ENUM macro instead of NS_ENUM. The Swift compiler recognizes this and doesn’t require switches to have a default case.