Custom measurement unit

Question

In iOS 10, Apple introduced several components for quantifying measurements. For example:

let velocity = Measurement(value: 3, unit: UnitSpeed.metersPerSecon         


        

Answer 1

Since the conversion is not linear, you will need to create your own UnitConverter subclass:

class UnitConverterInverse: UnitConverter {
    var coefficient: Double

    init(coefficient: Double) {
        self.coefficient = coefficient
    }

    override func baseUnitValue(fromValue value: Double) -> Double {
        return coefficient / value
    }

    override func value(fromBaseUnitValue baseUnitValue: Double) -> Double {
        return coefficient / baseUnitValue
    }
}

extension UnitSpeed {
    static let minutesPerKilometer = UnitSpeed(symbol: "min/km",
        converter: UnitConverterInverse(coefficient: 1000.0 / 60.0))
}

let velocity = Measurement(value: 60, unit: UnitSpeed.milesPerHour)

let velocity2 = velocity.converted(to: .minutesPerKilometer)

print(velocity2)

0.621371192237334 min/km