Open Radar

 
This is a duplicate of rdar://14251519 but I think is a very nice addition so please forwarding to the Clang team for the next version of Clang!

Summary:

It would be nice be able to flag designated initializers using an __attribute__, and have Clang emit a warning whenever they're not properly used. This is especially important as the rules for designated initializers are easily missed and error-prone.

Example:

@interface FooClass: NSObject
- (id) initWithFoo:(id)foo __attribute__((designated_initializer));
@end

@implementation FooClass
{
    id _foo;
}

- (id)initWithFoo:(id)foo_
{
    self = [super init];
    if(self) {
        _foo = foo_;
    }
    return self;
}
@end

@interface BarClass: FooClass
- (id) initWithBar:(id)bar;
@end

@implementation BarClass
{
    id _bar;
}

- (id) initWithBar:(id)bar_
{
    self = [super init]; // Clang would complain that FooClass's designated initializer isn't called
    if(self) {
        _bar = bar_;
    }
    return self;
}

@end


Notes:

This is somewhat related to __attribute__((objc_requires_super)), as designated initializers should be called or reimplemented by subclasses designated initializers.