Android Compose Generics Objects and Extensions

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Name of the Codelab or Codelab URL
https://developer.android.com/codelabs/basic-android-kotlin-compose-generics?hl=ja#6

Describe the problem
A clear and concise description of what the problem is.

In which lesson and step of the codelab can this issue be found?
Lesson number + step number.

7.11

fun main() {
    Quiz().printProgressBar()
}

↓

fun main() {
   val quiz = Quiz()
   quiz.printProgressBar()   
}