Request: for Kotlin, offer to replace "interface" with "fun interface" when possible

[AndroidDeveloperLB]

I think it's enough to just check if the number of functions in the interface is just one, not sure.

[Miha-x64]

Yes, but how this is useful?
AFAIK, the only reason to use fun interface is to enable SAM while avoiding boxing of primitives and inline classes. Is this a common scenario? Or what am I missing?

[AndroidDeveloperLB]

Aren't those advantages enough?
Also, it makes code shorter :)
I think most people don't even know about this. Having an inspection could encourage knowing about it.

[AndroidDeveloperLB]

Here, a talk about it:
https://stackoverflow.com/a/59446061/878126

[Miha-x64]

Still, why prefer fun interface over functional type? For example, the former cannot be inlined.
This gives me idea of another inspection: if a short non-recursive non-override function never touches anything private and accepts an instance of fun interface which is called in-place, the function should be marked as inline, and fun interface should be replaced with a functional type.

[AndroidDeveloperLB]

Can you please provide an example (code snippet) of when it isn't a nice thing to have?

[AndroidDeveloperLB]

I personally prefer it this way. I think on Java it's automatic, no?
Can you please at least make it optional?

[Miha-x64]

when it isn't a nice thing to have?

Well, there's no technical difference between fun interfaces and grumpy ones. What I mean is

interface A { fun run() }
fun interface B { fun run() }
typealias C = () -> Unit

inline fun a(/*actually noinline*/ a: A)
inline fun a(/*actually noinline*/ b: B)
inline fun a(c: C) // truly inline

NB: this is just an observation from the IDE behavior. I haven't found any official information about this.

[AndroidDeveloperLB]

By "noinline", you mean it's not inlined, right?

[Miha-x64]

Right, and Kotlin has an according soft keyword: noinline.

[AndroidDeveloperLB]

@Miha-x64 Oh I never used it. Sorry for that. Kotlin has some special keywords that I never used, and I don't think I even saw someone using...