AtomicKotlinCourse/Object-Oriented Programming/Nested Classes/Exercise 4/task.md

## Nested Classes (#4)

Improve the implementation of the *State* pattern in `Ticket.kt`. Change `Seat`
from an enumeration to a non-nested `abstract class`, with a nested subclass
for each `Seat` type. `Seat` contains `abstract` member functions for
`upgrade()` and `meal()`. There's also a `toString()` for `Seat` that produces
the `simpleName` of the specific subclass.

`Ticket` now becomes a simple holder for a `Seat` object, along with
`upgrade()` and `meal()` functions which forward their actions to the `Seat`
object.

Bonus (Challenging): Why can't you use delegation for `seat` in `Ticket`?

<sub> This task doesn't contain automatic tests,
so it's always marked as "Correct" when you run "Check".
Please compare your solution with the one provided! </sub>