Open Radar

 
Summary:

Assigning an instance variable through an expression statement will release the intermediate prematurely, and then crash as the now-deleted object is retained by the instance variable assignment.

Reduced case:

#import <Foundation/Foundation.h>

@interface Hej : NSObject { id level; } @end
@implementation Hej 
-(void)test;
{
    level = ({id temp = [NSObject new]; temp; });
}
@end

int main (int argc, const char * argv[]) {
    @autoreleasepool {
        [[Hej new] test];
    }
    return 0;
}

Regression:
Assigning to a local variable and then the ivar works fine.

Notes:
Compiler is "Apple LLVM Compiler 3.0".

You might also be asking yourself, "why are you using GCC compiler extensions? They make my head hurt.". I love expression statements, because they allow me to write things like:
  #define $notNull(x) ({ __typeof(x) xx = (x); NSAssert(xx != nil, @"Must not be nil"); xx; })

used like
  [dict setObject:$notNull([foo bar]) forKey:@"thing"];