kotlin - Using a class's properties without having to write its name down every time

Question

fun eval(expr: Expr): Int =
        when (expr) {
            is Num -> expr.value
            is Sum -> expr.left + expr.right
        }

interface Expr
class Num(val value: Int) : Expr
class Sum(val left: Expr, val right: Expr) : Expr

I would like to ideally use value, left, and right without having to call expr everytime. Is that possible?

question from:https://stackoverflow.com/questions/65911935/using-a-classs-properties-without-having-to-write-its-name-down-every-time

Answer 1

That's what the with scope function is for.

fun eval(expr: Expr): Int = with (expr) {
        when (this) {
            is Num -> value
            is Sum -> left + right
        }
    }