What does __bridge mean in objective c?

Question

I am following a tutorial in Core Graphics and I came across the code __bridge. I looked into it and saw that it had to do with ARC but I am confused on what it does. Could someone explain what it does in this context?

    void drawLinearGradient(CGContextRef context, CGRect rect, CGColorRef startColor, CGColorRef endColor)
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGFloat locations[] = { 0.0, 1.0 };

    NSArray *colors = @[(__bridge id) startColor, (__bridge id) endColor];

    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations);

}

It transfers ownership. And I hope there's more to that method or you have at least two leaks. — Kevin, Dec 31 '13 at 19:44
I suggest to read "Managing Toll-Free Bridging" in the [Transitioning to ARC Release Notes](https://developer.apple.com/library/mac/releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html) ! — Martin R, Dec 31 '13 at 19:47
@Kevin Not to split hairs, but `__bridge` explicitly does not transfer "ownership". As [Transitioning to ARC Release Notes](https://developer.apple.com/library/mac/releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html#//apple_ref/doc/uid/TP40011226-CH1-SW1) says "`__bridge` transfers a pointer between Objective-C and Core Foundation with no transfer of ownership." — Rob, Dec 31 '13 at 20:16

score 5 · Accepted Answer · edited Jan 02 '14 at 01:25

5

It's part of Automatic Reference Counting (ARC). From the docs:

__bridge transfers a pointer between Objective-C and Core Foundation with no transfer of ownership.

edited Jan 02 '14 at 01:25

Peter Hosey

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answered Dec 31 '13 at 19:54

highlycaffeinated

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What does __bridge mean in objective c?

1 Answers1