How do I change this List<T>? ```data class ...

# announcements

[Pablo]

How do I change this List<T>?

data class Foo (val id: String, val name: String)
val fooList = listof<Foo>(Foo("1","foo1"),Foo("2","foo22)

Imagine I get this fooList as a parameter and I want to update this list, do I need to do a clone of the list and then a copy of the data class and update there the values?

[gildor]

this is read only list with immutable data classes, so yes, you have to copy it to modify

[Pablo]

but if its comming via parameter to a fun then how do I update the val inside the list?

[gildor]

you cannot, you have to copy your Foo too

[gildor]

depends how you want to copy it, what it’s doing

[gildor]

if you want to modify every item of the list, it usually looks something like:

fun doSomething(list: List<Foo>) {
    val newList = list.map { foo ->
        foo.copy(name = foo.name.uppercase() )
    }
    println(newList)
}

[a_wer1986]

also you can convert list to mutable, modify it and convert it back to readonly one
something like this:

val list = listOf<Any>()
val mutList = list.toMutableList()
// TODO: apply changes to mutList, e.g. add or remove items
val result = mutList.toList()

[Pablo]

But if I need to do a find first? I mean I want to change just the Foo with a "foo1" I tried your proposals but when I do the if or find it says the value of copy is not used because could be that the list doesn't find the "foo1"

[Pablo]

Let's say I have this :

val list = List<Foo>

val foundValue = list.find{it.title == "foo1"}
Here I need to change the value of that value

[gildor]

still use map

[gildor]

it’s the easiest solution

[gildor]

list.map { if (it.title == “foo1) it.copy(…) else it }