Why is the getOrElse() function of arrow-kt returning Any?

Question

I am trying to understand the getOrElse() function of arrow-kt. I want to create a simple function that takes a list of strings, filters them, and returns the first matching value as an Option<String>. I created the following trivial example:

fun filterStrings(incoming: List<String>): Option<String> {
    val result = incoming.filter {
        it.contains('e')
    }.firstOrNone().getOrElse {
        incoming.filter {
            it.contains('b')
        }.firstOrNone()
    }

    return result
}

@Test
fun `test filter strings`() {
    val values = listOf("aad", "aba", "cdc", "bbb")
    val result = filterStrings(values)
    assertThat(result.isSome()).isTrue()
    assertThat(result.getOrBlank()).isEqualTo("aba")
}

In this example, the code will fail to compile since result is being smartcast to Any. Why is the result variable being smartcast to Any instead of Options<String>? Is there a way to work around this without doing an unsafe cast? I am aware that there are better ways to write a function like this, but I'm trying to get a handle on the fundamentals of what is happening.

tyg · Accepted Answer · 2025-11-19 21:51:26Z

2

getOrElse unwraps an Option and returns its value, respectively the default you provided when the value is missing.

So the return type of getOrElse is the union of the Option's type - here String - and the type of the default value - here Option<String>. Their nearest common supertype is Any, so that's the type of the return value here.

The documentation describes it as follows:

Returns the option's value if the option is nonempty, otherwise return the result of evaluating default.

answered Nov 19 at 21:51

tyg

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11 Comments

tyg Nov 19 at 22:09

We already covered that in the other question of yours. In short: There previously was orElse, but it was deemed too niche to warrant a dedicated function and was removed. The official recommendation is to use recover { alternative().bind() } instead. But as I said, all of that was already answered in the other question. What else do you want to know?

tyg Nov 20 at 15:27

@pbuchheit But what Slaw wrote is the same that I wrote as an answer to your previous question. That shouldn't have been new to you... I'm a bit confused.

Slaw Nov 20 at 22:37

@pbuchheit You say bind() wasn't necessary, but if that was the case then the original getOrElse would be working for you. The bind() call is inside the recover { ... } block. The recover function returns an Option. The bind() function essentially "unwraps" the inner Option (returned by the second call to firstOrNone) so that recover returns Option<String> instead of Option<Option<String>>.

Slaw Nov 20 at 22:41

@pbuchheit Also, I recommend incoming.firstOrNone { it.contains(...) } instead of incoming.filter { it.contains(...) }.firstOrNone(). The latter is likely to perform unnecessary work and creates an unnecessary intermediate list.

pbuchheit Nov 21 at 15:01

After I switched over to using firstOrNone() and bind() I got it to work. Thanks you for your help.

tyg Nov 21 at 15:26

@pbuchheit You seem to have forgotten that you already got that very same answer on your previous question: stackoverflow.com/a/79823950/6216216 -- Why did you ask the same here again in the comments, and why didn't you accept the answer over there?

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