Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

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

// Extension property on List
val <T> List<T>.lastIndex: Int
    get() = size - 1

// Extension on companion object (if class has one)
class Matrix(val rows: Int, val cols: Int) {
    companion object
}
fun Matrix.Companion.identity(n: Int): Matrix {
    // returns n×n identity matrix (simplified)
    return Matrix(n, n)
}

// Member extension — DSL pattern
class HtmlBuilder {
    private val sb = StringBuilder()

fun String.tag(name: String): String {
        sb.append("<$name>$this</$name>")
        return this
    }

fun build() = sb.toString()
}

fun buildHtml(block: HtmlBuilder.() -> Unit): String {
    val builder = HtmlBuilder()
    builder.block()
    return builder.build()
}

fun main() {
    println("level".isPalindrome)     // true
    println("kotlin".isPalindrome)    // false

val list = listOf(10, 20, 30)
    println("Last index: ${list.lastIndex}")   // 2

val m = Matrix.identity(3)
    println("${m.rows}x${m.cols} identity")   // 3x3 identity

val html = buildHtml {
        "Hello".tag("h1")
        "World".tag("p")
    }
    println(html)   // <h1>Hello</h1><p>World</p>
}