fun choice(vararg choices: DerAdapter<*>): DerAdapter<Pair<DerAdapter<*>, Any?>> {
    return object : DerAdapter<Pair<DerAdapter<*>, Any?>> {
      override fun matches(header: DerHeader): Boolean = true

      override fun fromDer(reader: DerReader): Pair<DerAdapter<*>, Any?> {
        val peekedHeader =
          reader.peekHeader()