Originally proposed and provided by Rob Rix allows you to append values from an NSArray to a Swift array, so long as they match the Swift array's expected element type.

Array+NSArrayAppend.swift

import Foundation

@assignment func += <T:AnyObject> (inout array: T[], cocoaArray: NSArray) {
    array.extend(
        map(cocoaArray) {
            $0 as T
        }
    )
}