Hello, I have a questions regarding transformation of list: ```val result = myList .filt...

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[PoisonedYouth]

Hello,
I have a questions regarding transformation of list:

val result = myList
            .filter { it.nullableProperty != null }
            .map { it.nullableProperty!!.fromAccount }

Why do I have to use the non-null asserted call in the map step?

[Joffrey]

This is because filter is generic and has the same type of element as output. The condition in the filter leads to a smart cast within the filter lambda, but that smart-cast type doesn't make it out.

This is why the stdlib introduced filterNotNull for exactly this purpose

[Szymon Jeziorski]

because filter does not change generic arguments type as shown by its signature:

public inline fun <T> Iterable<T>.filter(predicate: (T) -> Boolean): List<T>

Looking at your code you can achieve what you need explicitly calling map and then `filterNotNull`:

val result = myList
            .map { it.nullableProperty }
            .filterNotNull()
            .map { it.fromAccount }

But in your use case mapNotNull with safe access to fromAccount would fit perfectly achieving exactly the same:

val result = myList.mapNotNull { it.nullableProperty?.fromAccount }

[Roukanken]

(those two would have same result only if fromAccount is non-nullable; otherwise first one could return null, and second wouldn't)

[Szymon Jeziorski]

@Roukanken whoops, you're absolutely right, probably didn't have to rush so much with the comment :)

[PoisonedYouth]

The "fromAccount" property is non-null

[PoisonedYouth]

Thanks for your explanations