Is there any way to avoid the cast here? There is ...

# getting-started

[Marcin Wisniowski]

Is there any way to avoid the cast here? There is filterIsInstance() but it only works for the root element, not an inner property.

[Shawn]

No, not unless you were to also have subclasses of Foo that concretely specified Bar member types

[Marcin Wisniowski]

I guess I can just not use the filter and instead have an if check in the forEach, which gets me a smart cast.

[Shawn]

or when (it.bar) { is ... }

[mkrussel]

If you only need it.bar and not the rest of Foo you can do

listOf<Foo>()
   .mapNotNull { it.bar as? Bar.A)
   .forEach { a ->
   }

[Marcin Wisniowski]

I do need the rest of Foo unfortunately

[Marcin Wisniowski]

But that gave me an idea

[Marcin Wisniowski]

A little clunky though, but works

[Shawn]

I don't know if that really buys you much readability tbh

[Marcin Wisniowski]

Yeah, it probably doesn't

[Shawn]

it also involves n more allocations

[mkrussel]

I would probably just go back to a basic for loop with an if statement unless this was going to feed into more operators than just the forEach.

[Łukasz Gendek]

image.png

[Marcin Wisniowski]

I still need the other properties of Foo, which is why I couldn’t just map it to bar

[Łukasz Gendek]

now I see what you mean. Maybe this would help

[Łukasz Gendek]

image.png

[Shawn]

that's just a variation on the solution Marcin shared above... did you read the thread?

[Łukasz Gendek]

in my opinion this proposition is a bit better, please notice that that
• filterSecondNotNull is a generic, library method, and could be reused - it is not foo/bar related, in my opinion it doesn't make the code more complex, but opposite, it takes the complexity away
• what is left is much simplier now: the map expression is clearer, it is just an expression, with no statements e.g. return@mapOrNull

[phldavies]

Given the order of the pair isn't important in this chain, you could just as easily use .mapNotNull { (it.bar as? Bar.A)?.to(it) }