• mutableCollection의 element를 추가 / 삭제하는데 사용되는 operator

Adding elements

• add() / addAll() / + 등의 연산자가 활용 됨

fun sampleCodeForAddingElements() {
    val numbers = mutableListOf(1, 2, 3, 4)
    numbers.add(5)
    println(numbers)

    val numbersAddAll = mutableListOf(1, 2, 5, 6)
    numbersAddAll.addAll(arrayOf(7, 8))
    println(numbersAddAll)
    numbersAddAll.addAll(2, setOf(3, 4))
    println(numbersAddAll)

    val numbersPlusOperator = mutableListOf("one", "two")
    numbersPlusOperator += "three"
    println(numbersPlusOperator)
    numbersPlusOperator += listOf("four", "five")
    println(numbersPlusOperator)
}

Removing elements

• remove() / removeAll() / - 등의 연산자가 활용 됨
• retain() → operation 함수의 결과 값이 true 인 것만 남기고 나머지 element들은 제거

fun sampleCodeForRemovingElements() {
    val numbers = mutableListOf(1, 2, 3, 4)
    println(numbers)
    numbers.retainAll { it >= 3 }
    println(numbers)
    numbers.clear()
    println(numbers)

    val numbersSet = mutableSetOf("one", "two", "three", "four")
    numbersSet.removeAll(setOf("one", "two"))
    println(numbersSet)

    val numbersMinusOperator = mutableListOf("one", "two", "three", "three", "four")
    numbersMinusOperator -= "three"
    println(numbersMinusOperator)
    numbersMinusOperator -= listOf("four", "five")
//    numbersMinusOperator -= listOf("four")    // does the same as above
    println(numbersMinusOperator)
}