Can you explain what the use of the keyword crossinline in Kotlin means and in what cases it is applied?

In Kotlin, the keyword crossinline is used in the declaration of inline functions for lambda parameters to prevent the use of the return operator from the lambda, which attempts to exit the outer function.

When a function is marked as inline, lambda parameters can use return to exit the outer function (non-local return). But if the lambda is passed to another function or executed asynchronously, such a return is not possible.

crossinline prohibits non-local returns, allowing the lambda to be used safely in such contexts.

Example:

inline fun doSomething(crossinline action: () -> Unit) {
    val runnable = Runnable {
        action() // non-local return cannot be used here
    }
    runnable.run()
}

Here, crossinline ensures that action will not attempt to do a non-local return, preventing compilation errors.