` mapNotNull it foo filter barFunction it ` kotlinlang #getting-started

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karelpeeters

02/01/2019, 11:15 AM

.mapNotNull { it.foo }.filter { barFunction(it) }

👍 2

02/01/2019, 11:19 AM

this would give me a list of

foo

. I had intended to get a list of elements of

someList

Pavlo Liapota

02/01/2019, 11:22 AM

Can you just merge two `filter`s?

someList
.filter(it.foo != null && barFunction(it.foo))

foo

val

without custom getter, then this should work

👍 2

02/01/2019, 11:24 AM

yes that would work, thanks

Not sure if I like it better than using a double filter with !!, but I guess it is a bit cleaner

tddmonkey

02/01/2019, 11:45 AM

Could you make

barFunction

an extension method on a nullable receiver of the type in your list?

Then you could collapse it to:

someList
.filter(it.foo.barFunction())

Pavlo Liapota

02/01/2019, 11:47 AM

Or if receiver is not nullable, then

someList
.filter(it.foo?.barFunction() == true)

tddmonkey

02/01/2019, 11:49 AM

I mean make the extension on a nullable receiver, something like:

fun Fun?.barFunction() = this != null && barFunction(this)

Everything is null-safe and the call site is really clean

karelpeeters

02/01/2019, 11:51 AM

Except that the behavior wanted on null may be different depending on the caller.

tddmonkey

02/01/2019, 11:53 AM

Then that caller can define another extension method

02/01/2019, 12:06 PM

@tddmonkey good idea! In my case it would not work, unfortunately, as

barFunction

is already a method on a wrapper to a library. I guess my only option left is to overload barFunction on that wrapper

tddmonkey

02/01/2019, 12:12 PM

Hey @dG - I’m not sure if I’m being clear here. What I mean is in the scope of your filter method, define a private extension method. The fact it exists on a wrapper is fine!

02/01/2019, 12:16 PM

Aha! Thanks, I did not get that, now I do!

Nikky

02/01/2019, 1:57 PM

.filter { foo?.let { barfunction(it) } ?: false }

would be my sugestion

👍 1

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