hey all! Is there a way to create behaviour such ...

# announcements

[Simon Craigie]

hey all! Is there a way to create behaviour such as this without casting? I read that you can avoid unchecked cast exceptions with reified types but i can't seem to find a way to do this with function parameters:

fun <PARENT, CHILD: PARENT> returnFuncWithParentTypeAsParameter(resolver: (CHILD) -> Unit): (PARENT) -> Unit {
            return resolver as (PARENT) -> Unit
        }

Thanks in advance!

[Adam Powell]

What are you trying to do this for? This looks like an unsafe operation by definition unless you're planning to verify elsewhere that the parameter is of type CHILD when you call the resulting function.

[Simon Craigie]

The resulting function will only ever be called with a PARENT object. If all CHILD 's are of type PARENT 's then is it still unsafe?

[Robert Jaros]

inline fun <PARENT, reified CHILD: PARENT> returnFuncWithParentTypeAsParameter(crossinline resolver: (CHILD) -> Unit): (PARENT) -> Unit {
    return {
        if (it is CHILD) {
        	resolver(it)
        }
    }
}

[Robert Jaros]

This seems safe, has no cast and even works ;)

[Robert Jaros]

https://pl.kotl.in/QGS-LTeDp

[Adam Powell]

The reason it's unsafe without the explicit filtering @Robert Jaros demonstrated above is because while all `CHILD`s are of type PARENT, all `PARENT`s are not of type CHILD. If you pass any PARENT to a resolver that is expecting parameters of type CHILD, you are trying to make the latter assertion, which cannot hold.

[Simon Craigie]

ah of course. Thanks for clearing that up guys!