fast-enumeration.swift

// Before realizing that NSFastGenerator exists...

func enumerate(c: NSFastEnumeration) -> SequenceOf<AnyObject> {
    return SequenceOf<AnyObject> { () -> GeneratorOf<AnyObject> in
        
        let bufSize = 16
        
        var objects = UnsafeMutablePointer<AnyObject?>.alloc(bufSize)
        var state = NSFastEnumerationState()
        var currentCount = 0
        var currentIndex = 0
        
        return GeneratorOf<AnyObject> {
            if currentIndex >= currentCount {
                // Enumerate the next chunk of items
                currentIndex = 0
                currentCount = c.countByEnumeratingWithState(&state, objects: AutoreleasingUnsafeMutablePointer(objects), count: bufSize)
                if currentCount == 0 {
                    // Iteration is finished.
                    objects.dealloc(bufSize)
                    objects = nil
                    return nil
                }
            }
            return state.itemsPtr[currentIndex++]
        }
    }
}