C Style Formatting for Swift

format

func formatv(fstr : String, args : [CVarArgType]) -> String{
    var (res, af, i) = ("", "", 0)
    for c in fstr {
        if af == "" {
            if c == "%"{
                af = "%"
            } else {
                res += String(c)
            }
        } else {
            if c == "%"{
                if af == "%"{
                    af = ""
                    res += "%"
                    continue
                }
            }
            var lc = c
            switch c {
            case "s","@","d","i","u","o","x","X","f","F","e","E","g","G","a","A","c","p","n","v","j","J":
                break
            default:
                af += String(c)
                continue
            }
            if i < count(args){
                if lc == "j" || lc == "J" {
                    let indent = lc == "J"
                    if var jo: AnyObject = args[i++] as? AnyObject{
                        if NSJSONSerialization.isValidJSONObject(jo) {
                            if let data = NSJSONSerialization.dataWithJSONObject(jo, options: (indent ? NSJSONWritingOptions.PrettyPrinted : nil), error: nil) {
                                if let str = NSString(bytes: UnsafePointer<Int8>(data.bytes), length: data.length, encoding: NSUTF8StringEncoding){
                                    res += str as String
                                    af = ""
                                    continue
                                }
                            }
                        }
                    }
                    res += "?"
                } else if lc == "s" {
                    if let so = args[i++] as? NSString{
                        var data = NSMutableData(data: so.description.dataUsingEncoding(NSUTF8StringEncoding)!)
                        data.appendBytes("\0", length: 1)
                        res += String(format:af+String("s"), data.bytes)
                    }
                } else {
                    res += String(format:af+String(lc), args[i++])
                }
            } else {
                res += "?"
            }
            af = ""
        }
    }
    return res
}
func format(fstr : String, args : CVarArgType ...) -> String{
    return formatv(fstr, args)
}
func fprint(fstr : String, args : CVarArgType ...) {
    print(formatv(fstr, args))
}
func fprintln(fstr : String, args : CVarArgType ...) {
    println(formatv(fstr, args))
}

Standard C-style format specifiers for Swift.

Features

• String, NSString, Printable can be formatted using %s.
• JSON can be using %j. %J will indent the JSON. Only Arrays and Dictionaries are supported.

Examples

fprintln("Hello %s", "Tom")
let output = format("Touch %d times.", 15)
fprintln("JSON output: %j", ["Age":28,"Name":"Tom Tom"])