Marking plain -init to have a nullable return type without a warning

Question

I have an ObjC class inheriting from NSObject that wraps some third-party library macros so that I can use their functionality in Swift. The class has an ivar that's a container type from the library. Creation of the container can fail, and if it does, the instantiation of my class should fail too. So I marked -init as nullable.

@interface BasketWrapper : NSObject

/**
 * @abstract  Create an empty basket
 */
 - (nullable instancetype)init;    // ⚠️ Conflicting nullability specifier

@end

@implementation
{
    LibraryBasket * _basket;
}

- (instancetype)init
{
    self = [super init];
    if( !self ) return nil;

    // Can't really do anything without the wrapped item.
    _basket = LibraryBasket_Create();
    if( !_basket ) return nil;

    return self;
}

Unfortunately that -init declaration produces a compiler warning

Conflicting nullability specifier on return types, '_Nullable' conflicts with existing specifier 'nonnull'

pointing at NSObject's declaration.

As a workaround, I've marked the warning ignored with a pragma, and the method appears in Swift as failable.

Another option I considered was to mark plain -init unavailable and make a class method, +empty, instead. But then that's annoying because a) I can't use Swift initializer syntax, and b) init is unavailable in the class's own implementation too.

Is there some way to override the nullability of the inherited init without the warning?

Answer 1

You could declare a factory method having the same name as the type:

@interface BasketWrapper : NSObject

+ (nullable instancetype)basketWrapper;

/**
 * @abstract  Create an empty basket
 */
- (instancetype)init NS_UNAVAILABLE;

@end

This will make the warning go away and allow you to make use of the failable initializer.