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fun findUser(id: Int): String? { return if (id == 1) "Alice" else null } fun main() { val user: String? = findUser(2) // may be null // Safe call — returns null if user is null val length: Int? = user?.length println("Length: $length") // Length: null // Elvis operator — supply a default val displayName = user ?: "Guest" println("Hello, $displayName!") // Hello, Guest! // Chained safe calls val city: String? = null val upper = city?.trim()?.uppercase() println("City: $upper") // City: null // Not-null assertion (use sparingly) val known: String? = "Kotlin" println(known!!.length) // 6 // let block — runs only when non-null user?.let { println("User found: $it, length=${it.length}") } // Null check with smart cast if (user != null) { println(user.uppercase()) // user is String here } }
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