Hi, I need some help to understand what's going on...

# announcements

[AdalPari]

Hi, I need some help to understand what's going on with a lambda call to an interface.
I have the following interface in Java:

public interface ThreadExecutor {
    void execute(Runnable runnable);
}

Which I can call from Kotlin this way:

threadExecutor.execute { //code }

But, If I convert the interface to Kotlin, then I get an error in those calls, saying that they expect a Runnable but the return is Unit.

interface ThreadExecutor {
    fun execute(runnable: Runnable)
}

And I have to explicitly create the Runnable object.

threadExecutor.execute(Runnable { /* Code */ })

Would be great to understand why it happens, but also any idea on how to better solve it without having to create the Runnable in every call?

[thanksforallthefish]

it should be fixed in kotlin 1.4 with functional interface.

fun interface ThreadExecutor {
    fun execute(runnable: Runnable)
}

the magic work is fun 😄

[Rob Elliot]

Presumably you still need use ThreadExecutor from Java, hence continuing to take a Runnable rather than a () -> Unit?

[AdalPari]

Yes I need to define the argument as Runnable

[AdalPari]

I'll check that Marco.
Thanks both for the answers

[kralli]

Making ThreadExecutor a functional interface does not change anything in this example, because the SAM conversion is required for Runnable and not ThreadExecutor. However upgrading to 1.4 will solve this issue, as it widens the capabilities of SAM conversions in general.

[thanksforallthefish]

🤦 totally right Iven, I cannot even blame the morning, it was already 10ish here.

[AdalPari]

So, upgrading to Kotlin 1.4 will solve it without anything else? That would be great, thanks!