NSFastEnumeration over a C array crashing with BAD_ACCESS

Array.m

#import <Foundation/Foundation.h>

@interface Array : NSObject <NSFastEnumeration> {
	id __strong *_objs;
	NSUInteger _count;
}
@end

@implementation Array

-(id)init {
    self = [super init];
    if (self){
        _objs = (id __strong *)calloc(16,sizeof(*_objs));
    }
    return self;
}

-(void) addObject:(id)object {
	_objs[_count] = object;
	_count++;
}

-(id) objectAtIndex:(NSUInteger)index {
	return _objs[index];
}

- (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState*)state
                                   objects: (id __unsafe_unretained*)stackbuf
                                     count: (NSUInteger)len
{
    NSUInteger size = _count;
    NSInteger count;
    state->mutationsPtr = (unsigned long *)size;
    count = MIN(len, size - state->state);
    if (count > 0)
    {
        IMP imp = [self methodForSelector: @selector(objectAtIndex:)];
        int p = state->state;
        int i;
        for (i = 0; i < count; i++, p++) {
            stackbuf[i] = (*imp)(self, @selector(objectAtIndex:), p);
        }
        state->state += count;
    }
    else
    {
        count = 0;
    }
    state->itemsPtr = stackbuf;
    return count;
}

@end


int main(int argc, char *argv[]) {
    @autoreleasepool {
        Array *array = [Array new];
        [array addObject:@1];
        for (id object in array){    // BAD_ACCESS !
            NSLog(@"%@",object);
        }
    }
}

Solved at http://stackoverflow.com/questions/13184961/