You don't need to declare a custom class to have a singleton formatter, just use a global lazy var.

formatter.swift

var formatter: NSNumberFormatter  = {
    let f = NSNumberFormatter()
    f.locale = NSLocale.currentLocale()
    f.maximumFractionDigits = 2
    f.minimumFractionDigits = 2
    f.alwaysShowsDecimalSeparator = true
    f.numberStyle = .CurrencyStyle
    
    return f
}()

let a = formatter
let b = formatter

a === b // true