swift array extension

Array+safe.swift

extension Array {
    subscript (safe index: Int) -> T? {
        get {
            return indices(self) ~= index ? self[index] : nil
        }
        set (value) {
            if value == nil {
                return
            }

            if !(indices(self) ~= index) {
                NSLog("WARN: index:\(index) is out of range, so ignored. (array:\(self))")
                return
            }

            self[index] = value!
        }
    }
}