I am trying to understand how does this works. ```list.sortedWith(compareBy ({ when(it.state) { ...

# getting-started

[suhas]

I am trying to understand how does this works.

list.sortedWith(compareBy ({
    when(it.state) {
       A -> -1
       B -> 0
       C -> 1
   }
}))

This returns a list were all the elements with state A come first, followed by B and then followed by C. I am just not able to wrap head around this though. I understand how comparable works by overriding compareTo function and comparing two objects that the function gets. But not this. Can someone please explain this to me :)

[ephemient]

sortedWith(comparator) uses comparator.compare(a, b) instead of a.compareTo(b) as sorted() would use
compareBy(f).compare(a, b) returns f(a).compareTo(f(b))
you don't need sortedWith(compareBy()), there's a standard function

list.sortedBy {
    when(it.state) {
        A -> -1
        B -> 0
        C -> 1
    }
}

[suhas]

I am passing multiple selectors to compareBy , how can I use a and b when doing it in this to implement some complex logic?

[ephemient]

you can just implement Comparator { a, b -> ... } but what are you trying to do, it should not be common to need that

[CLOVIS]

Note that if your states are an enum class, it's already done for you: list.sortedBy { it.state } will sort them in the same order as they are declared in code.