We've been using tagged types in our code base but unfortunately they are not supported in the current codec generator macro.
Case classes having fields with tagged types are rejected by the Scala compiler simply because we cannot take `classOf` of a tagged type:
If it's acceptable as an enhancement, I'll be happy to submit a patch for this.
Just for completeness, tagged types are something like this:
They introduce additional compile-time type information without changing the runtime representation of values.
For more detailed introduction of tagged types please see e.g. here.