JuniorTheoryCommon

What does the program print?

KOTLIN

data class Point(val x: Int, val y: Int)

fun main() {
    val p = Point(1, 2)
    val q = p.copy(y = 5)
    println(q)
}

Point(x=1, y=5)

Expecting Point(x=1, y=2): thinking copy gives back an exact copy. A named argument in copy replaces that property in the new object.
Expecting Point@ and a hash: that is how a plain class prints. A data class generates toString, which lists every property as name=value.

JuniorTheoryCommon

KOTLIN

data class Point(val x: Int, val y: Int)

fun main() {
    val p = Point(1, 2)
    val q = p.copy(y = 5)
    println(q)
}

Point(x=1, y=5)

Expecting Point(x=1, y=2): thinking copy gives back an exact copy. A named argument in copy replaces that property in the new object.
Expecting Point@ and a hash: that is how a plain class prints. A data class generates toString, which lists every property as name=value.