Why does Kotlin compile `(Entity)->Boolean` to ...

# announcements

[Kroppeb]

Why does Kotlin compile (Entity)->Boolean to just a Function1<Entity, Boolean> and not to something that doesn't require boxing like `Predicate<Entity`>?

[Jakub Pi]

That's not enough to tell the input type of the function. Maybe you meant Predicate<Entity> with the implied Boolean return.

[Kroppeb]

Oof, yeah 🤦‍♂️
(Edited original msg)

[Jakub Pi]

You can always create your own:

typealias Predicate<T> = (T) -> Boolean

[Kroppeb]

No the issue is the boxing

[Jakub Pi]

Can't you inline your implementation of the predicate?

[Kroppeb]

No

[elizarov]

Compiling like that would have required a huge number of FunctionXxx interfaces to be included into the Kotlin standard library for all the combinations of pritimite types and still it would have been impossible to include all of them, but only a small subset. Better be pretictable here. In cases where you care avout boxing you can always define your own interface:

interface Predicate<T> {
    operator fun invoke(t: T): Boolean
}

However, I highly recommend to carefully measure the performance benefit of any such change in your code first. It actually helps much less often than it might seem to.

[Jakub Pi]

According to the article below, you can avoid the cost of boxing by replacing your predicate with a local function (instead of using a lambda). It might meet your needs: https://medium.com/@BladeCoder/exploring-kotlins-hidden-costs-part-2-324a4a50b70