Hello :wave::skin-tone-4: , Apologies if this is ...

# getting-started

[Helio]

Hello 👋🏽 ,

Apologies if this is a silly question, but would anyone be able to help me understand what this error Cannot use 'T' as reified type parameter. Use a class instead. means in this situation?

I’m trying to generalise the decodeFromString and encodeFromString but I’m confused why it doesn’t let me do that.

@ExperimentalLettuceCoroutinesApi
abstract class RedisDAO<T>(
    private val keyPrefix: String,
    private val ttl: Long, private val redisClient: BbcRedisClient
) {

    open suspend fun getValueFromKey(key: String): T? {
        val extractedValue = redisClient.getValueFromKey(key)
        return extractedValue?.let { Json.decodeFromString<T>(it) }
    }

    open fun buildRedisKey(identifier: String): String {
        return "$keyPrefix$identifier"
    }

    open suspend fun saveWithTTL(key: String, value: T) {
        val encodedValue = Json.encodeToString<T>(value)
        redisClient.storeKeyWithTTL(key, encodedValue, ttl)
    }
}

[Roukanken]

the probme is, that Json.encodeToString is a "reified inline function", eg, it's signature looks smth like this:

inline fun <reified T> encodeToString(...)

what this reified keyword means, is, that compiler will figure out what class T is, and the function can use T::class inside itself, as compiler will pass it to it.

Your problem is, that you are trying to pass this function T which is generics parameter of your class - that means you don't know what class T is, and neither compiler can figure it out. Which is why it's complaining

[Roukanken]

to solve it, you basically have to get KClass<T> from caller of this class, for example in constructor parameters.

I haven't exactly looked up how you can call encodeToString with KClass, but I a quick search at least shows function KClass<T>.serializer() which returns serializer for that class. That should be passable to encode afaik... Anyways, ya gotta look up other non-reified overloads of encode

(you can then create reified function as your "Fake" constructor, that will pass KClass or serializer to real constructor)

[Helio]

Thank you very much! I will have a careful look at what you said. I will post the solution if I figure.