How could I get the enum value using Android WorkM...

# getting-started

[dave08]

How could I get the enum value using Android WorkManager's Data::getString's value:

@ExperimentalStdlibApi
inline fun <reified T> Data.getValue(obj: Any?, prop: KProperty<*>): T {
    return when(T::class) {
        String::class -> getString(prop.name) as T
        Int::class -> getInt(prop.name, -1) as T
        Boolean::class -> getBoolean(prop.name, false) as T
        Enum::class -> getString(prop.name)?.let { enumValueOf<T>(it) } // This doesn't compile...
        else -> error("Trying to retrieve invalid type in Data for ${prop.name}: ${T::class}")
    }
}

[dave08]

The goal is to have something like:

enum Foo { BAZ, BAR }

class SomeData(val inputData: Data) {
   val dataEnumKeyForFoo: Foo by inputData // Saved as a string in Data with the key `dataEnumKeyForFoo` and the value one of the enum value's names...
}

[Javier]

obj is used for something?

[Joffrey]

I don't believe you can get type inference from this kind of when on the class of T (even with a reified T). This is why you needed to cast in the other cases.

I think you could use delegate providers instead of direct delegates. And for instance provide one for primitives and one for enums (with extra constraint on T : Enum<T> which will allow enumValueOf):

class SomeData(val inputData: Data) {
   val dataEnumKeyForFoo: Foo by inputData.enum()
   val otherProp: Int by inputData.primitive()
}

But you could even go as far as creating one for each primitive type too

[Joffrey]

@Javier I think that obj is necessary to conform to the delegate contract, even if not used

[Javier]

but what is the type?

[Joffrey]

The type of what?

[Javier]

because you, maybe, can

when(obj) {
    is String -> ... as T
    is Enum<*> -> ... as T
    else -> ... as T
}

[Joffrey]

I think obj is the instance of the class in which the property is declared, so it's not of type T. In the given example, obj would be of type SomeData

[dave08]

obj isn't needed, since such a class just contains a Data instance... the truth is, if I make that obj a DataProvider then I wouldn't need the receiver to be Data I could retrieve it from obj, but I don't think that would help too much...

[dave08]

So enum() would return a ReadWriteProperty implementation...?

[dave08]

I guess I can't avoid creating one instance per property per class...?

[dave08]

I can't use enumValueOf with (since it's not reified):

class EnumDataProperty<T : Enum<T>>(): ReadWriteProperty<Data, T> {
    override fun getValue(thisRef: Data, property: KProperty<*>): T {
        return thisRef.getString(property.name)?.let { enumValueOf(it) }!!
    }

    override fun setValue(thisRef: Data, property: KProperty<*>, value: T) {
        TODO("Not yet implemented")
    }
}

[dave08]

I guess not everything is so simple with delegate properties... set wouldn't work because it's a Data.Builder...

I ended up with:

inline fun <reified T : Enum<T>> Data.getEnum(key: String): T? =
    getString(key)?.let { enumValueOf<T>(it) }

inline fun <reified T : Enum<T>> Data.Builder.putEnum(key: String, value: T): Data.Builder {
    putString(key, value.name)

    return this
}

inline fun buildData(configure: Data.Builder.() -> Data.Builder): Data = Data.Builder().apply {
    configure()
}.build()