How can I be sure that casting is safe? Would the ...

# announcements

[Hullaballoonatic]

How can I be sure that casting is safe? Would the following be a completely safe cast, and thus not require a conversion function?

class Foo(vararg values: Int) : List<Int> by values.toList() {
    fun bar() = "foobar"
}

(listOf(1, 2, 3) as Foo).bar()

Casting is cheaper than conversion, because it doesn't require instantiating a new object, right?

[Marko Mitic]

It's cheaper but that cast wouldn't work, result of listOf() can never be cast to your custom implementation of List

[Marko Mitic]

you can cast it to List, and have bar as extension method

[Marko Mitic]

You don't even have to cast to List 🙂