Why does the compiler give me the error `TypeMisma...

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[kyleg]

Why does the compiler give me the error TypeMismatch in the onCreateViewHolder for both branches of the when ?

Return type is listed as the sealed class BaseHolder<PossibleRow> and the return types are both subclasses of the sealed class.

sealed class PossibleRow { /* objects A, B defined here */ }

sealed class BaseHolder<T: PossibleRow>(...): RecyclerView.ViewHolder(...) {
  class AHolder(...): BaseHolder<PossibleRow.A>(...)
  class BHolder(...): BaseHolder<PossibleRow.B>(...)
}

class LiftGroupRowAdapter {
  override fun onCreateViewHolder(..., viewType: Int): BaseHolder<PossibleRow> {
    return when(viewType) {
      0 -> BaseHolder.AHolder(...)
      1 -> BaseHolder.BHolder(...)
      else -> throw IllegalStateException("invalid viewType")
    }
  }
}

[Jordan Terrell]

override fun onCreateViewHolder(..., viewType: Int): BaseHolder<out PossibleRow>???

[Jordan Terrell]

Change the return type to BaseHolder<out PossibleRow>?

[kyleg]

Thanks. That got me almost there.

override fun onBindViewHolder(holder: BaseHolder<out PossibleRow>, position: Int) {
    holder.bind(sets[position])
  }

[kyleg]

Err, it did not have the out. I had to add the out in the parameter signature. Then I had to update the function to be:

override fun onBindViewHolder(holder: BaseHolder<out PossibleRow>, position: Int) {
    when(holder) {
      is BaseHolder.AHolder -> holder.bind(sets[position] as PossibleRow.A)
      is BaseHolder.BHolder -> holder.bind(sets[position] as PossibleRow.B)
    }
  }

[kyleg]

I can’t imagine why the out is needed, though. 😕