Question

I’m in the process of converting my project to using ARC. I have a category on NSColor with a method that returns an autoreleased CGColor representation:

@implementation NSColor (MyCategory)

- (CGColorRef)CGColor
{
    NSColor *colorRGB = [self colorUsingColorSpaceName:NSCalibratedRGBColorSpace];
    CGFloat components[4];
    [colorRGB getRed:&components[0]
               green:&components[1]
                blue:&components[2]
               alpha:&components[3]];
    CGColorSpaceRef space = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
    CGColorRef theColor = CGColorCreate(space, components);
    CGColorSpaceRelease(space);
    return (CGColorRef)[(id)theColor autorelease];
}

@end

What is the correct way to do this with ARC? I don’t want to return a retained CGColor.

The ARC converter in XCode suggest using

return (CGColorRef)[(__bridge id)theColor autorelease];

but that results in the following error message:

[rewriter] it is not safe to cast to ‘CGColorRef’ the result of
‘autorelease’ message; a __bridge cast may result in a pointer to a
destroyed object and a __bridge_retained may leak the object

Answer 1

CGColor is a Core Foundation object. You should not attempt to use autorelease with it. Instead, you should rename your method copyCGColor and return a retained object.

Auto-releasing is an Objective-C concept. It does not exist at the Core Foundation level.

Since CGColor is not toll-free bridged to any Objective-C class, it is very weird to try to autorelease it (even if that might work).

Update a few years later

There is now CFAutorelease() at the CoreFoundation level (available since Mavericks and iOS 7).