String Parsing (objc.io #9) in Swift - Example 2

stringparsing2.swift

// objc.io Issue #9
// February, 2014
// String Parsing by Chris Eidhof
//
// Example 2
// Swift version by Rob Hudson

import UIKit

let FormatError = 100
let MyErrorDomain = "io.objc.parsing"

let input: NSString = "backgroundColor = #ff0000\ntextColor = #0000ff"

func parse(input: NSString, inout error: NSError?) -> [String : String]? {
    let pattern = "(\\w+) = #([\\da-f]{6})"
    let expression = NSRegularExpression(pattern: pattern, options: nil, error: nil)
    let lines = input.componentsSeparatedByCharactersInSet(NSCharacterSet.newlineCharacterSet()) as! [NSString]
    var result = [String : String]()
    for line in lines {
        if let textCheckingResult = expression?.firstMatchInString(line as String, options: nil, range: NSMakeRange(0, line.length)) {
            let key = line.substringWithRange(textCheckingResult.rangeAtIndex(1))
            let value = line.substringWithRange(textCheckingResult.rangeAtIndex(2))
            result[key] = value
        } else {
            let message = "Couldn't parse line: \(line)"
            let errorDetail = [NSLocalizedDescriptionKey : message]
            error = NSError(domain: MyErrorDomain, code: FormatError, userInfo: errorDetail)
            return nil
        }
    }
    return result
}

var error: NSError?

if let output = parse(input, &error) {
    println(output)
} else {
    println(error)
}