Hi, I have a basic question. Can you hand me a lin...

# announcements

[jermainedilao]

Hi, I have a basic question. Can you hand me a link that explains the data type hierarchy when declaring a variable?

Lets say I have:

val list = mutableListOf<String>()

variable list will be a mutable list.

but if I have

val list: List<String> = mutableListOf<String>()

variable list will be an immutable list.

Can someone explain the hierarchy here? Is the defined variable data type always becomes the winning data type?

[diesieben07]

The 2nd list is not immutable. You could still do a cast to MutableList and modify it.

[diesieben07]

List is simply an interface that does not allow modification of the List, but it does not mean the object is actually immutable.

[thana]

https://kotlinlang.org/docs/reference/collections-overview.html

[Matthieu Stombellini]

MutableList (the real type of objects you get from calling mutableListOf) is a subtype of List. So all mutable lists are actually just lists with additional methods for modifying the list, and can be used where an immutable list (so a List object) is expected.

I'm not sure if that was clear.

[diesieben07]

Again, List is not immutable

[diesieben07]

It is read only

[thana]

the interface is simply YOUR view on the data. even without casting, someone else could change the collection although your view doesnt allow mutations

[diesieben07]

There is a very important difference

[jermainedilao]

Yes! All clear @diesieben07 & @thana Thanks!

[jermainedilao]

& @Matthieu Stombellini

[corneil]

using list you can only invoke functions of List<String>