I have a clock class and I think it would look nice to overload the `++` to call it's tick() method,...

# getting-started

[Ray Rahke]

I have a clock class and I think it would look nice to overload the ++ to call it's tick() method, like clock++. However it looks like Kotlin says that the inc operator overload needs to return a new copy of the object, instead of mutate? Why? Is that how this behavior always works? I just want to mutate the clock's internal .now/.elapsed/.delta etc. Returning a new copy of the clock seems wasteful as I am going to call this function hundreds of times every few seconds

[ephemient]

you can think of x++ as

val tmp = x
x = x.inc()
tmp

and ++x as

x = x.inc()
x

the prefix and postfix forms aren't defined independently as they are in C++

[ephemient]

since the expression x++ evaluates to the previous value of x, it isn't something that can easily be done by mutating in-place

[ephemient]

in your case, I'd just use a non-operator fun inc() for in-place mutation

[Ray Rahke]

fun inc() you mean `clock.inc()`` ?

[Ray Rahke]

so no overload

[ephemient]

yeah as a member function (or possibly an extension fun)

[ephemient]

correct

[Ray Rahke]

alright well what about things I make that function as collections of stuff

[Ray Rahke]

I have a player.inventory that just wraps over a mutable set

[Ray Rahke]

so an Inventory class

[Ray Rahke]

I would like to be able to do player.inventory += sword

[Ray Rahke]

just as I can do with the native set

[Ray Rahke]

mutableSetOf() += sword

[Ray Rahke]

is it creating a copy when I do it with the native sets?

[Ray Rahke]

or is it mutating

[ephemient]

depends on what's in scope

[Ray Rahke]

i assumed set += was equivalent to set.add()

[ephemient]

val x = mutableSetOf<Int>()
x += 1 // x.plusAssign(1)

var x = setOf<Int>()
x += 1 // x = x + 1 // x = x.plus(1)

[ephemient]

this is documented in https://kotlinlang.org/docs/operator-overloading.html#augmented-assignments