case unbounded
Continue to add to the buffer, treating its capacity as infinite.
case bufferingOldest (Int)
When the buffer is full, discard the newly received element.
バッファがいっぱいである時、新しく受け取った要素を廃棄します。
case bufferingNewest (Int)
When the buffer is full, discard the oldest element in the buffer.
バッファがいっぱいである時、バッファにおいて最古の要素を廃棄します。