How to represent magnitude for mass in Swift?

Question

// SI units
enum Magnitude : Measurement {
    case Milli = Measurement(-3, \"ml\")
    case Centi = Measurement(-2, \"cl\")
    case Desi = Measurement(-1, \"dl\")
         


        

Answer 1

Depending on what you need, maybe you can combine an enumeration of SI unit scales and the example in the Computed Properties section of Apple Swift Programming Guide. In this simplistic scheme all of input measurements would be stored in the same units (grams in this example). Then you would convert to whatever units you needed in the output.

It is very readable.

enum SI {
    case kg
    case hg
    case dag
    case g
    case dg
    case cg
    case mg

    var scale: Double {
        switch self {
        case kg:  return    0.001
        case hg:  return    0.01
        case dag: return    0.1
        case g:   return    1.0
        case dg:  return   10.0
        case cg:  return  100.0
        case mg:  return 1000.0
        }
    }
}

extension Double {
    var kg:  Double {return self * 1000.0}
    var hg:  Double {return self *  100.0}
    var dag: Double {return self *   10.0}
    var g:   Double {return self}
    var dg:  Double {return self *    0.1}
    var cg:  Double {return self *    0.01}
    var mg:  Double {return self *    0.001}

    func convertTo(si: SI) ->  Double {return self * si.scale}
}

Example: