var temperatureReference : [TemperatureReference] = [] {
    didSet {
        print("Temperature reference values =", temperatureReference)
    }
}

var tempRef1 = TemperatureReference(celcius: 12, fahrenheit: 35)
temperatureReference.append(tempRef1) // Calls didSet
let tempRef2 = TemperatureReference(celcius: 11, fahrenheit: 33)
let tempRef3 = TemperatureReference(celcius: 10, fahrenheit: 32)
temperatureReference.append(tempRef2) // Calls didSet
temperatureReference.append(tempRef3) // Calls didSet
temperatureReference[0].transposeCelciusToFahrenheit() // DOES NOT call didSet
tempRef2.transposeCelciusToFahrenheit() // DOES NOT call didSet
temperatureReference[2].celcius = 52 // DOES NOT call didSet