val list = listOf(1, 2, 3)

val mutableList = list.toMutableList()
mutableList.add(4)

• listOf() 는 List 인터페이스 타입을 리턴
• toMutableList()는 JVM에서 ArrayList 타입을 리턴
• mutableListOf() 도 ArrayList 타입을 리턴

val names: SortedSet<FullName> = TreeSet()
val person = FullName("AAA", "AAA")
names.add(person)
names.add(FullName("Jordan", "Hansen"))
names.add(FullName("David", "Blanc"))

println(names) // [FullName@63961c42, FullName@65b54208, FullName@1be6f5c3]
println(person in names) // true
println(person) // FullName@63961c42

person.name = "ZZZ"
println(names) // [FullName@63961c42, FullName@65b54208, FullName@1be6f5c3]
println(person in names) // false
println(person) // FullName@63961c42

• https://kotlinlang.org/docs/keyword-reference.html#hard-keywords is used as an infix operator to check that a value belongs to [a range](<https://kotlinlang.org/docs/ranges.html>), a collection, or another entity that [defines a 'contains' method](<https://kotlinlang.org/docs/operator-overloading.html#in-operator>).

기억하고 싶은 부분들

• data 클래스의 copy()

data class User(
	val name: String,
	val surname: String
)

• 두가지 모두 변경 가능

val list1: MutableList<Int> = mutableListOf()
var list2: List<Int> = listOf()

list1 += 1 // list1.plusAssign(1)
list2 += 1 // list2 = list2.plus(1)