This is correct behavior. In Swift, a subclass is not required (or expected) to inherit its superclass's initializers, whereas in Objective-C it usually is. The best we can do is crash at runtime.

…well, actually, I suppose we could do better by marking the initializer unavailable in the subclass in the generated header.

Comment by Thomas Torp (JIRA)

I expected it to be the correct behavior 🙂 But as you said it would be really great if the initializer is unavailable in the subclass 🙂

I think the generate header file should look like this:

SWIFT_CLASS("_TtC17TestProject13SomeBaseClass")
@interface SomeBaseClass : NSObject
@property (nonatomic, readonly, copy) NSString * __nonnull type;
- (nonnull instancetype)init __unavailable;
- (nonnull instancetype)initWithType:(NSString * __nonnull)type OBJC_DESIGNATED_INITIALIZER;
@end

SWIFT_CLASS("_TtC17TestProject12SomeSubClass")
@interface SomeSubClass : SomeBaseClass
- (nonnull instancetype)init __unavailable;
- (nonnull instancetype)initWithType:(NSString * __nonnull)type __unavailable;
- (nonnull instancetype)initWithOtherValue:(NSString * __nonnull)otherValue OBJC_DESIGNATED_INITIALIZER;
@end

Also every function that is marked as private override should be explicitly attributed as __unavailable in the generates header file.

You can't mark something private override for exactly that reason. You're not allowed to violate Liskov substitutability ("a subclass can be used where the superclass is expected") at compile-time except by using @available. I don't think we print @available either, though.

I agree with the general pattern, though I would add a message to the unavailable attribute.

Yeah, sorry, I meant every initializer marked as private override should be __unavailable. A message is fine.

What message should go with the unavailable attribute? I'm not able to come up with anything that adds anything meaningful beyond the default "'foo' is unavailable". We certainly can't suggest a different initializer because the compiler doesn't know what other initializer would be appropriate as a suggestion.

Submitted as PR #3852.

Comment by Thomas Torp (JIRA)

Eridius (JIRA User) I feel that unavailable message is the right choice. Thanks for solving this issue 🙂

Merged in 0473e99.