Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// Extension on String
fun String.isPalindrome(): Boolean {
    val cleaned = this.lowercase().filter { it.isLetter() }
    return cleaned == cleaned.reversed()
}

fun String.wordCount(): Int = this.trim().split("\\s+".toRegex()).size

// Extension on Int
fun Int.factorial(): Long {
    require(this >= 0) { "Factorial undefined for negative numbers" }
    return if (this <= 1) 1L else this * (this - 1).factorial()
}

// Extension on a list
fun <T> List<T>.secondOrNull(): T? = if (size >= 2) this[1] else null

// Extension on nullable type
fun String?.orEmpty2(): String = this ?: ""

// Extension with generic receiver
fun <T : Comparable<T>> T.clamp(min: T, max: T): T = when {
    this < min -> min
    this > max -> max
    else       -> this
}

fun main() {
    println("racecar".isPalindrome())   // true
    println("Hello World".isPalindrome())  // false
    println("The quick brown fox".wordCount())  // 4

println(5.factorial())   // 120
    println(0.factorial())   // 1

println(listOf(10, 20, 30).secondOrNull())   // 20
    println(emptyList<Int>().secondOrNull())       // null

val name: String? = null
    println(name.orEmpty2())   // ""

println(15.clamp(0, 10))    // 10
    println(-5.clamp(0, 100))   // 0
    println(50.clamp(0, 100))   // 50
}