Swift Inheritance problems generics

Question

I Need to be able to call a method of the generic type, so that I can have the value of a constant SENSOR_ID from SensorDescBattery. The method I use if called getSensorId() But when I call that function using generic type sensorDescBattery, it asks me for a parameter to the method getSensorId(),but it does not have one.

I have presented the class SensorDescBattery below:

class SensorDescBattery: SensorDescSingleValue {


    let SENSOR_ID : UInt64 = 0x0000000000000001 { get{ return SENSOR_ID}}

    var sensorIdentifier: Int64 = 0x0000000000000001

    var timestamp: UInt64
    var batteryPercent: Float
    var isCharging: Bool
    var isUsbCharge: Bool
    var isAcCharge: Bool

    init(timestamp: UInt64, batteryPercent: Float, isCharging: Bool, isUsbCharge: Bool, isAcCharge: Bool) {

        self.timestamp = timestamp
        self.batteryPercent = batteryPercent;
        self.isCharging = isCharging;
        self.isUsbCharge = isUsbCharge;
        self.isAcCharge = isAcCharge;
    }

    /*
        override keyword always needed here
    */
    required init(sensorData: SensorUploadSensorData) {

        self.timestamp = sensorData.recordTime
        self.batteryPercent = sensorData.valueFloat[0]
        self.isCharging = sensorData.valueBool[0]
        self.isUsbCharge = sensorData.valueBool[1]
        self.isAcCharge = sensorData.valueBool[2]
    }

    init (battery: UIDevice, timestamp: UInt64) {
        self.timestamp = timestamp
        self.batteryPercent = battery.batteryLevel
        if UIDeviceBatteryState.Charging.rawValue == 3{
            self.isCharging = true
            self.isUsbCharge = false
            self.isAcCharge = true
        }
        else {
            self.isCharging = false
            self.isUsbCharge = false
            self.isAcCharge = false
        }
    }

    /*
        Override keyword needed
    */
    func toProtoSensor() -> SensorUploadSensorData {

        let builder = SensorUploadSensorData.builder()

        /*
            Always set the record time! also it's important to put the values in the
            array in the same exact order as in Android
        */
        builder.recordTime = timestamp
        builder.valueFloat = [self.batteryPercent]
        builder.valueBool = [self.isCharging, self.isUsbCharge, self.isAcCharge]

        return builder.build()
    }

    func getSensorId() -> UInt64 {
        return SENSOR_ID;
    }

    func getValue() -> Float {
        return self.batteryPercent;
    }
}

Here is the class QueryNumSingleValue:

class QueryNumSingleValue {

var List : Array<SensorUploadSensorData>

func getSensorID() -> UInt64{
    fatalError("Must Override")
}
init(from timestamp_from :UInt64,to timestamp_to : UInt64){
    let vm = NervousVM()

    self.List = vm.retrieve(0, fromTimeStamp: 0, toTimeStamp: 0)
    self.List = vm.retrieve(getSensorID(), fromTimeStamp: timestamp_from, toTimeStamp: timestamp_to)
    if(containsReading()){
        println("retreived list of size /(getCount())")
    }
}


func getCount() -> Int
{
return List.count
}

This is SensorDescSingleValue

protocol SensorDescSingleValue : SensorDesc {

func getValue() -> Float

}

What I am trying to do is the following :

class SensorQueriesBattery<T : SensorDescBattery> : QueryNumSingleValue<SensorDescBattery>{

    override func getSensorID() -> UInt64 {
        return T.getSensorId()
    }

}

But it does not let me. How can I proceed?

Jhonpi · Accepted Answer · 2015-05-23 18:09:04Z

2

The compiler is asking you for a parameter because you are using the Class and not the object to call the method (and the method is no static) in this part of the code:

override func getSensorID() -> UInt64 {
    return T.getSensorId()
}

You should read more about generics in swift

One way to make your code works with your approach is:

class SensorQueriesBattery<T : SensorDescBattery> : QueryNumSingleValue{

    var batteryDesc: T

    init(desc:T) {
        self.batteryDesc = desc
    }

    override func getSensorID() -> UInt64 {
            return self.batteryDesc.getSensorId()
    } 
}

You have to pass the Generic object in the init to be able to call the method getSensorId()

answered May 23, 2015 at 18:09

Jhonpi

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4 Comments

Rob Over a year ago

OP can just do some more reading about generics in general, this is an issue that haunts all implementations of them that I have seen (C++, Java, Swift).

LoveMeow Over a year ago

I tried your method,and all the lines give the error QueryNumSingleValue needs a generic type within <...>

Jhonpi Over a year ago

@LoveMeow Have you changed the definition of QueryNumSingleValue class as a generic? if so, you have to set the generic when inherits from ´QueryNumSingleValue´.

LoveMeow Over a year ago

I tweaked it a bit, like you said the problem was not creating an object!

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