Implementation of NSFastEnumeration on top of CFBinaryHeap. The only way to get objects from CFBinaryHeap is to use allocated object buffer, but NSFastEnumeration doesn’t provide a way to free() it explicitly. I used autoreleased NSMutableData to manage the buffer and it somehow works.

CFBinaryHeap.m

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id __unsafe_unretained [])providedBuffer count:(NSUInteger)providedLength {
    // If this is not first invocation, finish by returning 0.
    if (state->state != 0) {
        return 0;
    }
    let count = CFBinaryHeapGetCount(self->_underlayingHeap);
    
    // We are empty.
    if (count == 0) {
        return 0;
    }
    
    // We can only get all objects at once into a pre-allocated buffer. This doesn’t work nicely with NSFastEnumeration.
    __autoreleasing var data = [[NSMutableData alloc] initWithLength:count * sizeof(id)];
    CFBinaryHeapGetValues(self->_underlayingHeap, data.mutableBytes);
    
    // The autoreleased NSData will live long enough to provide the underlaying buffer until for-in loop finishes.
    state->state = count;
    state->itemsPtr = (id __unsafe_unretained *) data.mutableBytes;
    state->mutationsPtr = data.mutableBytes; // Required to be non-nil.
    
    return count;
}