NSArray+Bifurcate.m

typedef BOOL (^ FilterBlock)(id _);

@implementation NSArray (Bifurcate)

- (void)bifurcate:(FilterBlock)test passing:(out NSArray **)passing failing:(out NSArray **)failing
{
    NSMutableArray * passed = [NSMutableArray array];
    NSMutableArray * failed = [NSMutableArray array];
    
    for (id thing in self) {
        if (test(thing)) {
            [passed addObject:thing];
        }
        else {
            [failed addObject:thing];
        }
    }
    
    *passing = passed;
    *failing = failed;
}

@end