Hey there. I got a situation where I must filter o...

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[Doru N.]

Hey there. I got a situation where I must filter out some items from a read only list which represents property of an object.
A more visual representation of the nested classes would be like this:

data class DataSourceResponse(val response: Response)
data class Response(val notifications: List<Notification>)
data class Notification(id: Int)

I have a function which takes a DataSourceResponse as a param and a callback, which should return a modified DataSourceResponse, filtering out some of the notifications from it.
How should I implement this filtering and copy, considering the given model classes above. (immutable notifications list).
The closest I got, was doing something like this:

callback.onDataLoaded(
    paramDataSourceResponse.copy (
        response = paramDataSourceResponse.response.copy (
            notifications = paramDataSourceResponse.response.notifications.filter { check(it) }
        )
    )
)

but it looks kinda ugly to me. Also, not having every class made data class, would make it even uglier. Are there any other solutions for this?

[hho]

Please use triple backticks around code blocks: https://get.slack.help/hc/en-us/articles/202288908-Format-your-messages#inline-code

[hho]

Thank you.
I'm not sure I understand – how can the inner Response be a copy of the paramDataSourceResponse as well?

[Pavlo Liapota]

If you don’t have any other properties in your data classes then this should be fine:

DataSourceResponse(Response(paramDataSourceResponse.response.notifications.filter { check(it) }))

[Doru N.]

@Pavlo Liapota yeah.. I have many other properties.. that was just to showcase the situation.

[Doru N.]

@hho DataSourceResponse is a wrapper class over Response, having some other properties as well

[Pavlo Liapota]

he means you have a type in your code example
you should have
paramDataSourceResponse.response.copy (
instead of
paramDataSourceResponse.copy (
in your second copy() call

[hho]

@Doru N. I think you were missing a .response in your inner copy.

[hho]

Best I can come up with is going explicit:

val filteredNotifications = paramDataSourceResponse.response.notifications.filter { check(it) }
val filteredResponse = paramDataSourceResponse.response.copy(notifications = filteredNotifications)
val filteredDataSourceResponse = paramDataSourceResponse.copy(response = filteredResponse)
callback.onDataLoaded(filteredDataSourceResponse)

[Pavlo Liapota]

Or maybe you can use run or let functions:

paramDataSourceResponse.run {
    copy(response = response.run {
        copy(notifications = notifications.filter { check(it) })
    })
}

[Doru N.]

@hho oh, ok, didn’t see that

[Doru N.]

@Pavlo Liapota appreciate your opinions, but I think using those functions are useless, when you only have a copy function call inside