Hello all, I need help coming up with a way to upd...

# getting-started

[liminal]

Hello all, I need help coming up with a way to update one of the existing MySection items in MyPost: Any help will be greatly appreciated

data class MyPost(
val somePostAttr: String,
val rows: List<MyRow>
)

data class MyRow(
val someRowAttr: String,
val columns: List<MyColumn>
)

data class MyColumn(
val someColumnAttr: String,
val sections: List<MySection>
)

data class MySection(
val someSectionAttr: String
)

[Sam]

Can you elaborate a bit? Since your properties are all immutable, any “update” would mean creating a new instance of MyPost. My first thought is that a simple solution would involve several nested calls to copy. If you want something a bit smarter you could look at #arrow Optics.

[liminal]

Yeah I will need to create a copy of MyPost and can’t seem to get the code right to do that

[liminal]

The starting point is fun MyPost.update(section: MySection): MyPost

[Sam]

How will you determine which section should be updated? Is the new section just appended to the column, or does it replace one of the existing sections?

[liminal]

Replace. Forgot to add a property id: String to MySection in the code above

[Sam]

👍

[Sam]

Here’s my version:

val newPost = post.copy(
    rows = post.rows.map { row ->
        row.copy(columns = row.columns.map { column ->
            column.copy(sections = column.sections.map { oldSection ->  
                if (oldSection.id == newSection.id) newSection else oldSection
            })
        })
    }
)

[Sam]

So much nesting 😬 😄

[Sam]

I guess it would be possible to make a more efficient version that doesn’t copy the rows or columns that don’t contain the target section

[liminal]

Thank you so much Sam! It’s so simple now that I am looking at it :) really appreciate it. Have a great day