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data class Config(
    var host: String = "localhost",
    var port: Int = 8080,
    var debug: Boolean = false
)

fun main() {
    // apply — configures an object, returns the object
    val config = Config().apply {
        host  = "example.com"
        port  = 443
        debug = true
    }
    println(config)

// let — transforms a nullable value, returns lambda result
    val name: String? = "  Kotlin  "
    val length = name?.let {
        val trimmed = it.trim()
        println("Trimmed: '$trimmed'")
        trimmed.length
    }
    println("Length: $length")

// run — execute block, return result; also used on an object
    val summary = config.run {
        "Connecting to $host:$port (debug=$debug)"
    }
    println(summary)

// also — side effect, returns the original object
    val numbers = mutableListOf(3, 1, 4, 1, 5)
        .also { println("Before sort: $it") }
        .also { it.sort() }
        .also { println("After sort: $it") }

// with — group calls (not an extension, receiver = this)
    val message = with(StringBuilder()) {
        append("Hello")
        append(", ")
        append("Kotlin!")
        toString()
    }
    println(message)
}