Why is there no ByteString => T deserializer?

I can do redis.set("key", MyCustomType(42)) as long as I have a valid RedisValueConverter in implicit scope for my custom type.

But when I do redis.get("key") all I get is a raw Option[ByteString] and I have to convert it back to my custom type myself.

Why is there not a get[T: RedisValueDeserializer](key: String): Future[Option[T]] with some basic support for common types (Strings, Ints, Longs, Booleans, Lists, Sets, Maps, etc.)? Then I can have my own RedisValueDeserializer in scope to deserialize my custom types.

[agemooij]

The problem is in this call:

redis.getT(k)

This call does not specify the desired outcome type T so the compiler will look for an unambigious implementation of the type class and finds two instead of one. The solution is to call the method like this:

redis.getT[String](k)

If you plan to only provide the two default implementations you have now, then there would be a variation of the same trick that would help make it possible to call get without a type parameter, namely:

@implicitNotFound(msg = "Cannot find ByteStringDeserializer type class for ${T}")
trait ByteStringDeserializer[T] {
  def deserialize(bs: ByteString): T
}

object ByteStringDeserializer extends LowPriorityDefaultByteStringDeserializerImplicits

trait LowPriorityDefaultByteStringDeserializerImplicits extends LowerPriorityDefaultByteStringDeserializerImplicits {
  implicit object stringDeserializer extends ByteStringDeserializer[String] {
    def deserialize(bs: ByteString): String = bs.utf8String
  }
}

trait LowerPriorityDefaultByteStringDeserializerImplicits {
  implicit object byteStringDeserializer extends ByteStringDeserializer[ByteString] {
    def deserialize(bs: ByteString): ByteString = bs
  }
}

Also don’t forget to add the @implicitNotFound annotation because it will help end users to find out what they are doing wrong (i.e. the forgot to create a deserializer for their custom type).

[darshoka]

why empty list " List() " is returning while using redis.get(“myKey”) ?