拡張プロパティ

extended_property.kt

val String.lastChar: Char
    get() = get(length - 1)

var StringBuilder.lastChar: Char
    get() = get(length - 1)
    set(value: Char) {
        this.setCharAt(length - 1, value)
    }

/*

>>>println("Kotlin!".lastChar)
!
>>>val sb = StringBuilder("Kotlin?")
>>>println(sb)
Kotlin?
>>>sb.lastChar = '!'
>>>println(sb)
Kotlin!

*/