Hi. I'm using delegates outside of fields. This pr...

# announcements

[eirikb]

Hi. I'm using delegates outside of fields. This produces a warning ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE upon assignment only. While that warning is technically correct, and makes sense, it would be nice to remove it. How?
My code looks like this:

var ok by okProp
ok = true

where setting ok will have side effect. Example: https://pl.kotl.in/81eXfsXLG (press run to get the warnings).
On a side note, the decompiled code looks like this:

KProperty var1 = $$delegatedProperties[0];
ReadWriteProperty ok = okProp;
ok.setValue((Object)null, var1, true);

As one would expect the variable will be both accessed and assigned, just not in Kotlin

[Dave K]

I’m not sure I understand the use case. The warning is because ok is instantiated but never used.

Adding
if (ok) println(“ok”)
Makes the warning go away

And the same warnings appear with

var t: Boolean
t = true

I think also if you return ok from some function it would similarly not provide the warning. Essentially you’re instantiating this variable without any purpose?

[eirikb]

It has purpose, since it has side effects. Imagine the delegate is passed into a function, and inside that function by is used only to trigger it

[Dave K]

I am still not seeing why a delegate with side effects instead of a lambda or similar https://pl.kotl.in/IA98W8-qm

That said, I suppose you could suppress the warning if you really want to use delegate and don’t want the warning https://pl.kotl.in/3Dp2hzVcP

Just trying to understand the use case to suggest something that wouldn’t produce a warning to begin

[eirikb]

That's a good solution, thanks.
If you wonder about why I would pass around a delegate instead of a lambda; it's handy. I pass it from a library without knowing if a consumer would listen or set the value. I also support multiple listeners and binding. And it works very well in JavaFX (if consumer uses that). Maybe it's an anti-pattern, or an anti-pattern to be, but from my point of view it's neat

[Dave K]

You’d want to suppress UNUSED_VALUE if you want to suppress the second warning https://pl.kotl.in/Q3Ffo8WC2

[eirikb]

Got it. Thank you

[eygraber]

This comes up a lot in multiplatform Kotlin Gradle where you typically see things like:

val commonMain by getting

With commonMain not being used after the declaration

[eirikb]

Yeah isn't that default in the build.gradle.kts (template) file when creating a new project? I'm not sure if those lines are required though, would it fail if removed? As in the template have them just in case

[eygraber]

I think there are side effects to the delegate, so IIRC it is required

[eirikb]

Did a quick test. By having code in "commonMain" all I needed to do to support JavaScript was to have js under kotlin. I could safely remove val jsMain by getting . But yes it could have side effects, very similar to my case