Swift – String with comma-separator to double

Use the decimalSeparator:

let formatter = NSNumberFormatter()
formatter.decimalSeparator = ","
let grade = formatter.numberFromString("2,3")

if let doubleGrade = grade?.doubleValue {
    print(doubleGrade)
} else {
    print("not parseable")
}

Prints

2.3

'pure' Swift (no Foundation)

let str = "9,8"
let sstr = str.characters.split(",").joinWithSeparator(["."])
if let d = Double(String(sstr)) {
    print(d) // 9.8
}