[tmail21]

Yes, but the resulting object is not a "List" and hence would not inter-operate with any function that took a List as input.

In essence if the original object implements a List _interface_, then the new one should as well. If you do all of this, then you've essentially implemented immutability and structural sharing. But then you have to do this for 10 other Collection types as well.

Now, you could do all this, but I could do it as well and do it differently. Then my function which took MyList as argument would not interoperate with your function that wants to pass YourList as argument.

Something as fundamental as an (immutable) collection needs to be standardized so that all functions can take these and return them and thus compose easily.

This is the case with languages that implement immutability like Elixir, Haskell etc.

[jorgemf]

There are already interfaces for Immutable collections in kotlin. And all the functional operators as map, filter, etc, returns them. But it is not true immutability as you said, because under the hood they are normal list. They aren't even read-only objects, but you encapsulate this behaviour under an interface.