Hi all, I'm using operator overloading and have is...

# announcements

[Gilles Barbier]

Hi all, I'm using operator overloading and have issues with inheritance, with

open class MyInt(open var int: Int = 0) : {
    operator fun plus(increment: Int): MyInt = MyInt(int + increment)
}

I can do

MyInt(4) + 3

It works. But now, I would like to extends MyInt

class OtherInt(override var int: Int = 0) : MyInt(int)

I can do OtherInt(4) + 3 but the output is a MyInt. Is there a way for OtherInt to benefit from operator overloading without reimplementing it in it?

[diesieben07]

https://pl.kotl.in/VvDqEohua

[Gilles Barbier]

thx @diesieben07 I have extended your solution 🙂
https://pl.kotl.in/NeOYppqtn

[diesieben07]

Your plus operator is modifying the instance now and not creating a new one. Just fyi

[Gilles Barbier]

your are right ! 🤔

[Gilles Barbier]

surprisingly, your solution (and my extension) do work in playgroung but not in real life (Intellij Idea)

[diesieben07]

I've tried mine in IntelliJ and it works.

[Gilles Barbier]

hmm, ok strange, thx for letting me know

[diesieben07]

What errors do you get?

[Gilles Barbier]

MyInt(3) + 3 is not accepted, saying that none of .plus definition match this one

[diesieben07]

Can you show the code you have in IntelliJ?

[Gilles Barbier]

if I put the line
operator fun <T : MyInt> T.plus(increment: Int): T = this.copy(int + increment) as T on main file it works

[diesieben07]

You'll have to import it

[Gilles Barbier]

but if I put this line with classes definitions it does not work anymore

[Gilles Barbier]

very strange

[diesieben07]

Why? its a method like all others

[Gilles Barbier]

I know I do not understand

[Gilles Barbier]

if you are curious https://www.loom.com/share/a098927abfee432f9376190c5b8f782b

[diesieben07]

Like I said, you need to import the function for it to be visible

[Gilles Barbier]

oh! import com.zenaton.commons.data.plus I did not know that

[Gilles Barbier]

thank you very much

[Gilles Barbier]

For the record, here is the working version https://pl.kotl.in/MkAGYbzvU

[diesieben07]

IntelliJ should suggest that with alt-enter on the plus or even when you autocomplete with ctrl-space

[diesieben07]

it very much behaves like a normal method call

[Gilles Barbier]

A last question, do you know why

operator fun invoke() = this

is ok, but

operator fun invoke() = { return this }

is not?

[diesieben07]

the = sign means "return the expression on the right hand side". So the 2nd is trying to return { return this }

[diesieben07]

The equivalent of the first with a block body would be operator fun invoke() { return this }, without =

[Gilles Barbier]

sorry, I meant

operator fun invoke() { return this }

It does not work

[diesieben07]

When you specify a body for the function like that you need to explicitly state the return type, you cannot let the compiler infer it:
operator fun invoke(): ReturnTypeHere { return this }

[Gilles Barbier]

hmm ok - thank you very much for your help. I've learnt a lot