How can I add element in specified index and if the index exist element, replace it. ```val list = ...

# getting-started

[Simon Lin]

How can I add element in specified index and if the index exist element, replace it.

val list = mutableListOf<String>()

list.add(0, "a")
list.add(0, "b")

list.toString() // except [b], actual [b, a]

[gildor]

use list[0] = “b”

[gildor]

it’s the same as list.set(0, “b”)

[Simon Lin]

How about the a? If call list[0] = “a” will cause exception

[Simon Lin]

Is there a convenient way for each insert without check the list

[gildor]

What is your use case? I’m just not quite sure what if you real life example for this

[gildor]

If you just need a function which does ” add element in specified index and if the index exist element, replace it.“, there is no such function in stdlib, it’s probably better just to create own extension for this

[gildor]

Still curious about your use case for this

[Simon Lin]

I need to show the list data according to its index
and the user can add data into the list.

first, the list is empty. User can only inset to 0 index
then, user can choose to insert data to the end or selected the data that insert early and replace its value.

[gildor]

But insert is not replace

or selected the data that insert early and replace its value.

I think no need to overthink this, it’s just easy to check if there is item and set it

[Simon Lin]

ok ty 😀

[Simon Lin]

I was affect by the SQL The INSERT OR REPLACE Statement.

[gildor]

Problem that there is no built-in transaction on list unlike database, checking for “contains” is a separate operation from add/set, so it cannot be done in a safe way under the hood of the list, only for thread safe list implementations, which are not used by default, because of performance penalty