You can do what you want with generics. However, to use generics we first need to extract that giant block of code into a method:
val positions: Array<PositionJson>? get() = getPositions()
fun getPositions(): Array<PositionJson>? {
...
}
We haven't solved the problem, but now we're in a position to be able to solve it by making getPositions generic (note that I also rename the function):
val positions: Array<PositionJson> get() = getArrayOf<PositionJson>()
// thanks to type inference I can omit the type on getArrayOf if desired:
val positions: Array<PositionJson> get() = getArrayOf()
fun <T> getArrayOf(): Array<T>? {
val service = constructServiceURL(POSITIONS, null, true)
try {
val messageJson = mapper.readValue<MessageJson<Array<T>>>(
callURL(service),
object: TypeReference<MessageJson<Array<T>>>() {
})
val error = messageJson.error
if (error != null) throw AccountsAPIException(error.errorCode, error.description)
return messageJson.data
} catch (e: Exception) {
throw AccountsAPIException(e)
}
}
Perfect! Except this won't compile thanks to type erasure. But we can fix this too by making the function inline and making the type parameter reified:
inline fun <reified T: Any> getArrayOf(): Array<T>? {
...
}
And that should do it. Now you can reuse this function as needed:
val positions: Array<PositionJson>? get() = getArrayOf()
val persons: Array<PersonJson>? get() = getArrayOf()
val bananas: Array<BananaJson>? get() = getArrayOf()
inline fun <reified T: Any> getArrayOf(): Array<T>? {
val service = constructServiceURL(POSITIONS, null, true)
try {
val messageJson = mapper.readValue<MessageJson<Array<T>>>(
callURL(service),
object: TypeReference<MessageJson<Array<T>>>() {
})
val error = messageJson.error
if (error != null) throw AccountsAPIException(error.errorCode, error.description)
return messageJson.data
} catch (e: Exception) {
throw AccountsAPIException(e)
}
}
One last thing: note that in all my examples I used property getters (get() = ...) as in your original code. However, I strongly suspect that you do NOT want to use a getter. Getters will be called every time someone accesses your property, which in this case means that every time someone reads the positions property you'll be calling constructServiceURL and making the service call, etc. If you want that code to only happen once then you should just call getArrayOf() once and assign the result to your property:
val positions: Array<PositionJson>? = getArrayOf()
// this syntax would also work:
val positions = getArrayOf<PositionJson>()
