Person

this

enum class

override fun toString()

data class Color(val r: Int, val g: Int, val b: Int) {
    init {
        require(r in 0..255) { "invalid red $r" }
        require(g in 0..255) { "invalid red $g" }
        require(b in 0..255) { "invalid red $b" }
    }

    constructor(r: String, g: String, b: String) : this(r.toColorComponent("red"), 
                                                        g.toColorComponent("green"), 
                                                        b.toColorComponent("blue"))
}

private fun String.toColorComponent(name: String) = toIntOrNull() ?: throw IllegalArgumentException("Color component $name string is not a number: $this")

vararg

lazy { }

inline fun <reified T> testException() {
        try {

        } catch (e: T) { // ERROR: reified type is forbidden for catch parameter

        }
    }

Kotlin has features for null safety

Kotlin is langage that has null safety characteristic.

Kotlin is null safety language

Kotlin has null safety.

listOf("str", "str", 2, "str")

.class

listOf(listOf("str", "str"), listOf(2), listOf("str"))