and here is my implementation in `FunctorFilter`: ```. /** * Apply a filter to a structure such t...

# arrow-contributors

[thanh]

and here is my implementation in `FunctorFilter`:

. /**
   * Apply a filter to a structure such that the output structure contains all instances of specified class.
   */
  @Suppress("UNCHECKED_CAST")
  fun <A, B> Kind<F, A>.filterIsInstance(klass: Class<B>): Kind<F, B> =
    filterMap { a -> if(klass.isInstance(a)) Some(a as B) else None }

[Imran/Malic]

@pakoito is that your intended function ?

[aballano]

shouldn't it be a kotlin's KClass instead?

[Imran/Malic]

How does filterIsInstance look like in the stdlib?

[thanh]

Here it is

/**
 * Returns a list containing all elements that are instances of specified class.
 */
public fun <R> Iterable<*>.filterIsInstance(klass: Class<R>): List<R> {
    return filterIsInstanceTo(ArrayList<R>(), klass)
}

[thanh]

and

/**
 * Appends all elements that are instances of specified class to the given [destination].
 */
public fun <C : MutableCollection<in R>, R> Iterable<*>.filterIsInstanceTo(destination: C, klass: Class<R>): C {
    @Suppress("UNCHECKED_CAST")
    for (element in this) if (klass.isInstance(element)) destination.add(element as R)
    return destination
}

[pakoito]

I'm with @aballano, why not KClass?

[pakoito]

for Java classes too, it seems

[pakoito]

(?)

[pakoito]

I'm surprised it's not inline + reified, I'm sure I'd seen filterIsInstance<Bla>()

[thanh]

I think filterIsInstance should be the same interface with the filterIsInstance in stdlib

[pakoito]

take a Kind and returns a Kind

[pakoito]

no implicit list conversion

[pakoito]

nah I don't like the stdib one, too much runtime magic

[pakoito]

we have filter and filterMap for this

[pakoito]

I like your initial one

[thanh]

I'm confused now 😄 what should I change in my implementation? Switch to KClass?

[Imran/Malic]

dont use the magic in the stdlib

[pakoito]

/**
   * Apply a filter to a structure such that the output structure contains all instances of specified class.
   */
  @Suppress("UNCHECKED_CAST")
  fun <A, B> Kind<F, A>.filterIsInstance(klass: Class<B>): Kind<F, B> =
    filterMap { a -> if(klass.isInstance(a)) Some(a as B) else None }

[pakoito]

this works

[pakoito]

now my question is, whether klass should be Class or KClass, and if you could test with a Java file to see which one works

[pakoito]

as a test 😄

[aballano]

but the above doesn't work for him it seems, the generated extension functions are missing the right Class import

[aballano]

https://kotlinlang.slack.com/archives/C8UK6RTHU/p1571131514011600

[Imran/Malic]

Maybe a refresh would do it

[thanh]

I tried to clean build but it didn't work