Swift number formatting

Question

I am just starting to get to know Swift but I am having a serious problem with number formatting at an extremely basic level.

For example, I need to display an integer w

Answer 1

There is a simple solution I learned with "We <3 Swift", which is so easy you can even use without Foundation, round() or Strings, keeping the numeric value.

Example:

var number = 31.726354765
var intNumber = Int(number * 1000.0)
var roundedNumber = Double(intNumber) / 1000.0

result: 31.726

Answer 2

You can still use good ole NSLog("%.2f",myFloatOrDouble) too :D

Answer 3

Here's a POP solution to the problem:

protocol Formattable {
    func format(pattern: String) -> String
}
extension Formattable where Self: CVarArg {
    func format(pattern: String) -> String {
        return String(format: pattern, arguments: [self])
    }
}
extension Int: Formattable { }
extension Double: Formattable { }
extension Float: Formattable { }

let myInt = 10
let myDouble: Double = 0.01
let myFloat: Float = 1.11

print(myInt.format(pattern: "%04d"))      // "0010
print(myDouble.format(pattern: "%.2f"))   // "0.01"
print(myFloat.format(pattern: "$%03.2f")) // "$1.11"
print(100.format(pattern: "%05d"))        // "00100"

Answer 4

You can construct a string with a c-like formatting using this constructor:

String(format: String, arguments:[CVarArgType])

Sample usage:

var x = 10

println(String(format: "%04d", arguments: [x])) // This will print "0010"

If you're going to use it a lot, and want a more compact form, you can implement an extension like this:

extension String {
    func format(arguments: [CVarArgType]) -> String {
        return String(format: self, arguments: arguments)
    }
}

allowing to simplify its usage as in this example:

"%d apples cost $%03.2f".format([4, 4 * 0.33])