C++ father tell me that JAVA is built on top of C++, so what language is Kotlin built on? everyone.

# compiler

[anlex N]

C++ father tell me that JAVA is built on top of C++,
so what language is Kotlin built on? everyone.

[dmitriy.novozhilov]

https://youtu.be/Ljr66Bg--1M?si=PpZNJ4JHv_yllBA0▾

[anlex N]

when generate android apk, kotlin compile path is: Kotlin -> Java byte code -> apk?

[anlex N]

can Kotlin do "pass by reference" like C++?

[dmitriy.novozhilov]

Everything is passed by reference by default

[dmitriy.novozhilov]

Exceptions are primitive types and value classes

[anlex N]

can you update this [Gemini answer](https://gemini.google.com/app/f1ce571ade99913c)?

[dmitriy.novozhilov]

AI is not reliable source of information

[Klitos Kyriacou]

It's misleading to say "Everything is passed by reference by default". Kotlin is like Java when it comes to parameter passing. So, for example,

fun foo(list: MutableList<String>) {
    list = arrayListOf<String>("bar")
}

If Kotlin was "pass by reference" in the same way as C++ and C#, then the above function foo would change the passed parameter list to a list containing an element "bar". But Kotlin is not pass-by-reference in this way. You can't change the value of a passed variable.

I think what Dmitriy meant was that variables (except primitives) hold a reference to an object. So even though you pass the value of a variable to a function, that value is the reference of the object.

[dmitriy.novozhilov]

References to parameters are immutable (non-reassignable)
The code from your snippet won't compile

[anlex N]

@Klitos Kyriacou show me your code playground, please

[anlex N]

@Klitos Kyriacou @dmitriy.novozhilov how to realize the same effort for "pass by reference" like C++ in the Kotlin?

[Klitos Kyriacou]

You have to be explicit in Kotlin, using for example a wrapper object: let's say you want a function that changes a passed value, then you have to keep that value inside an object:

class Wrapper<T>(var value: T)

fun foo(x: Wrapper<Int>) {
    x.value = 456
}

int main() {
    val x = Wrapper(123)
    foo(x)
    check(x.value == 456)
}

This is not idiomatic Kotlin. In Kotlin, we prefer to keep things immutable, so we would probably in the above case just write a function that takes one value and returns another value, rather than mutating.

[anlex N]

as your code, x is like "pass by value" in the C++. x is "pass by value" in the C++ in the fact.

[anlex N]

this do not have performance. teacher.

[anlex N]

what's solution?

[Arjan van Wieringen]

Why doesn’t it have performance?

[anlex N]

if no reference, it is performance problem.