apply और with: कॉन्फ़िगर करें और लौटाएँ

class Config {
    var host: String = ""
    var port: Int = 0
}
fun makeConfig(): Config {
    // Without apply:
    // val c = Config(); c.host = "x"; c.port = 8080; return c
    return Config().apply {
        host = "localhost"
        port = 8080
    }
}
fun main() {
    val c = makeConfig()
    println("${c.host}:${c.port}")
}

class Builder {
    val parts = mutableListOf<String>()
}
fun main() {
    val result = Builder().apply {
        parts.add("hello")
        parts.add("world")
    }.parts.joinToString(" ")
    println(result) // hello world
}

class Rect(val w: Int, val h: Int)
fun main() {
    val area = with(Rect(3, 4)) {
        w * h
    }
    println(area) // 12
}

class Box(var width: Int = 0, var height: Int = 0)
fun main() {
    val box = Box().apply { width = 10; height = 20 } // returns Box
    val area = with(box) { width * height }            // returns Int
    println("$box area=$area")
}

fun main() {
    val list = mutableListOf<String>().apply {
        add("a")
        add("b")
        add("c")
    }
    println(list)
}

class Sb {
    private val buf = StringBuilder()
    fun append(s: String): Sb { buf.append(s); return this }
    fun build(): String = buf.toString()
}
fun main() {
    val s = Sb().apply {
        append("Hello, ")
        append("Kotlin!")
    }.build()
    println(s)
}

class Person(val name: String, val age: Int)
fun main() {
    val description = with(Person("Ada", 35)) {
        "Name: $name, Age: $age, AgeNext: ${age + 1}"
    }
    println(description)
}

class Address {
    var city: String = ""
    var zip: String = ""
}
class User {
    var name: String = ""
    var address: Address = Address()
}
fun main() {
    val u = User().apply {
        name = "Ada"
        address.apply {
            city = "Istanbul"
            zip = "34000"
        }
    }
    println("${u.name} in ${u.address.city}")
}

class Config(val host: String, val port: Int)
fun main() {
    // Named arguments often beat builder + apply:
    val cfg = Config(host = "localhost", port = 8080)
    println("${cfg.host}:${cfg.port}")
}