rangeOverride.swift

extension String {
    func getUnicodeIndex()->Int {
        return Int(self.unicodeScalars[self.unicodeScalars.startIndex].value)
    }
    static func getUnicodeRangeFrom(from:Int, to:Int, closedRange:Bool)->String {
        let step = from > to ? -1 : 1;
        let final = closedRange ? to + step : to
        let chars = Int[]((from..final).by(step)).map{String(UnicodeScalar($0))}
        return "".join(chars)
    }
}

@infix func .. (left: String, right: String) -> String {
    return String.getUnicodeRangeFrom(
        left.getUnicodeIndex(),
        to:right.getUnicodeIndex(),
        closedRange:false)
}

@infix func ... (left: String, right: String) -> String {
    return String.getUnicodeRangeFrom(
        left.getUnicodeIndex(),
        to:right.getUnicodeIndex(),
        closedRange:true)
}

let s1 = "三".."丏" // "三上下丌不与"
let s2 = "z"..."j"  // "zyxwvutsrqponmlkj"