with — Scope an Existing Object

data class Order(val id: Int, var status: String, var paidAt: Long?)

fun main() {
    val order = Order(42, "pending", null)

    // Multi-step mutation/access on the same object
    with(order) {
        status  = "paid"
        paidAt  = System.currentTimeMillis()
        println("Order $id is $status")
    }

    // with as expression: returns the last value
    val summary = with(order) {
        "Order $id paid at $paidAt"
    }
    println(summary)

    // Useful for chained API calls on Java objects
    val sb = StringBuilder()
    with(sb) {
        append("Hello, ")
        append("world!")
        append(" — ")
        append(42)
    }
    println(sb)
}