objc_independent_class.m

#import <Foundation/Foundation.h>

@protocol OS_Foo <NSObject> @end
typedef NSObject<OS_Foo> * Foo;

@protocol OS_Bar <NSObject> @end
typedef NSObject<OS_Bar> *__attribute__((objc_independent_class)) Bar;

@interface Test : NSObject
@end

@implementation Test

+ (NSArray *)newArray
{
    NSArray *array = nil;
    return array; // No warning: 'NSArray *' is not overridden
}

+ (NSObject *)newObject
{
    NSObject *object = nil;
    return object; // Incompatible pointer types returning 'NSObject *' from a function with result type 'Test *'
}

+ (Foo)newFoo
{
    Foo foo = nil;
    return foo; // Incompatible pointer types returning 'Foo' (aka 'NSObject<OS_Foo> *') from a function with result type 'Test *'
}

+ (Bar)newBar
{
    Bar bar = nil;
    return bar; // No warning: 'Bar' is not overridden as it is marked as objc_independent_class
}

@end