[KT-6300]: Stdlib: add findIs and firstIs method

[Komdosh]

There is a find and filterIs methods for iterables, but there is no method for finding one specific element in iterable.

For example:

val services = listOf<CommonInterface>(specificInterfaceA, specificInterfaceB, specificInterfaceC)

val specificService = services.findIs<SpecificInterfaceB>()

it is easy to implement, but it is still not in stdlib.

public inline fun <reified R> Iterable<*>.findIs(): R? {
    return find { element -> element is R } as R?
}

Forgotten for 11 years actually: KT-6300

[Komdosh]

Any issues, suggestions?

[MukjepScarlet]

Shouldn't this
public inline fun <reified R> Iterable<*>.firstIs(): R? {
be
public inline fun <reified R> Iterable<*>.firstIs(): R {
?
Because it throws exception if no instance of R found.

[MukjepScarlet]

By the way Sequence also needs this.

[Komdosh]

Shouldn't this public inline fun <reified R> Iterable<*>.firstIs(): R? { be public inline fun <reified R> Iterable<*>.firstIs(): R { ? Because it throws exception if no instance of R found.

Fixed, thanks!

[Komdosh]

This was rejected