I must admit my mind was blown :exploding_head: Who can explain to me what’s exactly is going on her...

# announcements

[igor.wojda]

I must admit my mind was blown 🤯
Who can explain to me what’s exactly is going on here?

[Dmitry]

Class Survey is created.

It is extended from List, because author want it to have all the functionality that list have.

But we don’t want to implement that all by ourselves.

So we delegate all of those methods on List interface that to actual list with by keyword.

[Dmitry]

This allows us to have our own type “Survey” that we can use accross project, while having all the goodies of it being also a “List” without manually delegating all methods from List interface to underlying list.

[Dmitry]

Alternative would be (if you are more of a show me a code guy):

[Dmitry]

(and so on, manually delegating everything by-hand to private property)

[Matteo Mirk]

Igor you may want to read about delegates: https://kotlinlang.org/docs/reference/delegation.html

[wbertan]

Besides the class Survey also guarantee it will have at least one item in the list.

[Vampire]

And that it is a read-only list.
The result of listOf could easily be cast to MutableList and modified usually.

[Animesh Sahu]

The result of listOf could easily be cast to MutableList and modified usually.

Atleast on JVM, I remembered, listOf() returns Arrays.asList which throws runtime exceptions if you try to add or remove something. However it does let you replace items.

[Vampire]

Indeed, it's a fixed size list

[juliocbcotta]

That is a bad implementation that gets a lot of attention. Are you sure that you want to have all API from list in your survey? You most likely are exposing too much API. The version with a NonEmptyList class as parameter allow a much more elegant solution where you have control of the exposed API