Hey everyone! Today I finally started using sealed classes, which is great. But I came to a point wh...

# announcements

[Philipp Mayer]

Hey everyone!
Today I finally started using sealed classes, which is great. But I came to a point where I'm not sure how to handle it in the correct way:

.map { (payment, requestModel) -> steps.performRequest(payment, requestModel) 
.filter { (_, result) -> result is ApiResult.Success }
.map { (payment, result) -> steps.update(payment, result) }

After performing the request, I want to filter out all results which were not of Type ApiResult.Success
Unfortunately the compiler does not allow this, since update() is expecting ApiResult.Success .
What did I miss there?
My only solution right now is to set the result Parameter to ApiResult and add a require() block in my update function, but I'm not really happy with that.

[gsala]

You can use .filterIsInstance<ApiResult.Success>()
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/filter-is-instance.html

[Philipp Mayer]

I totally forgot about that. Thanks! But forwarding to that: I'm returning Pair<Payment, ApiResult> , that method would also filter out the payments.

[Vampire]

If update always requires success, why is it a parameter?

[Vampire]

And if you need it for whatever reason, just do not give result but simply hard-coded success, as you filter before that only success payments are left

[Philipp Mayer]

ApiResult.Success carries the responseData, which is needed for the update.

[Philipp Mayer]

That's can't be seen in the code snippet, sorry about that.

[Vampire]

Ah, I see

[Vampire]

Then cast it?

[Vampire]

result as Success

[Philipp Mayer]

How to do that in the filter method without losing the corresponding payment?

[Philipp Mayer]

I could make payment a property of Result, but that wouldn't be the cleanest solution.

[Philipp Mayer]

Well, the last mapping step in that workflow only logs the output, so I just use a guard clause inside update(): if (result !is ApiResult.Success) return

[muliyul]

Hopefully you meant return@map there

[Vampire]

I don't understand what you mean Philipp, what is wrong with my suggestion?

[Vampire]

.map { (payment, requestModel) -> steps.performRequest(payment, requestModel) 
.filter { (_, result) -> result is ApiResult.Success }
.map { (payment, result) -> steps.update(payment, result as ApiResult.Success) }

AS you filtered for only the pairs that have success there, it should always succeed properly

[Philipp Mayer]

No, you're completely right Björn! I was just so focused on the filter method that I didn't even think about using it as input parameter to update. 😄

[Philipp Mayer]

Thanks a lot guys!

[Arian Stolwijk]

.mapNotNull { it as? FooBar } is usually nice too

[Vampire]

How would that help here?

[Vampire]

Can you give the full example?