Are Kotlin `MutableList`s implemented like a linked list under the hood? Can I pop/append from both...

# getting-started

[Chris Cordero]

Are Kotlin `MutableList`s implemented like a linked list under the hood? Can I pop/append from both ends or from the middle cheaply? Or is this an expensive calculation

[Dominaezzz]

MutableList is an interface without implementation.

[Dominaezzz]

Usually the implementation is an ArrayList but that is up to you.

[Dominaezzz]

You might want to look at the new ArrayDeque.

[Chris Cordero]

You mean I can specify an implementation when I write mutableListOf()?

[Dominaezzz]

Haha nope. That is an ArrayList. What I meant is that you can have multiple implementations of MutableList .

[Chris Cordero]

Oh I see

[Chris Cordero]

I didn't realize that MutableList was an interface, but it was in the docs staring at me the whole time lol

[Chris Cordero]

Not trying to disprove you, but I can't find docs that indicate it would be an ArrayList though

[Chris Cordero]

Is this something you just kinda have to know about the language?

[Dominaezzz]

Yes, it's not guaranteed to be an ArrayList I guess, but looking at the source code.... we know it is 🙂.

[Chris Cordero]

Got it! Thank you very much

[diesieben07]

If you absolutely want an array list, use arrayListOf