What does '==' mean?

1

– code –

class Car(val color: String)

fun main() {

    val car1 = Car(“red”)

    val car2 = Car(“blue”)

    val car3 = Car(“red”)

    if (car1 == car2) {

        println(“car1-car2: same”)

    } else {

        println(“car1-car2: different”)

    }

    if (car1 == car3) {

        println(“car1-car3: same”)

    } else {

        println(“car1-car3: different”)

    }

    val x: Int = 100

    val y: Int = 100

    if (x == y) {

        println(“x-y: same”)

    } else {

        println(“x-y: different”)

    }

    if (x === y) {

        println(“x-y: same”)

    } else {

        println(“x-y: different”)

    }

}

/*

car1-car2: different

car1-car3: different

x-y: same

x-y: same

Process finished with exit code 0

 */
– code –

I expected ‘car1-car3: same’.
I thought car1 and car3 are the same as structurally.

2

You should read the documentation. It is thoroughly explained there. As for your example. Add data keyword to your Car class and it will behave like you expect. Your Car is not a value-type so it is compared by reference, not by value.

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3