val initialization before superclass constructor

http://scala-programming-language.1934581.n4.nabble.com/Constructor-vooo...

-jason

On Mon, Jun 28, 2010 at 7:54 AM, Alex Hvostov wrote:
> I've noticed that Scala 2.8 seems to no longer initialize fields before
> calling the superclass constructor, unlike 2.7.
>
> Consider the following REPL code:
>
> ---code---
> class C1 {
>        val field = "C1"
>        println("Hi, I'm " + field)
> }
>
> class C2 extends C1 {
>        override val field = "C2"
> }
>
> new C1
> new C2
> ---end code---
>
> In Scala 2.7.7, this code prints:
>
> ---output---
> Hi, I'm C1
> Hi, I'm C2
> ---end output---
>
> This is what I intend.
>
> However, in 2.8.0.RC6, this code instead prints:
>
> ---output---
> Hi, I'm C1
> Hi, I'm null
> ---end output---
>
> This is *not* what I intend, and it seems to be because C2 overrides the
> generated method 'field', but doesn't initialize its generated field
> 'field' until after C1's constructor is called. As a result, field
> 'field' is null -- neither "C1" nor "C2" -- at the time C1's constructor
> is called.
>
> Is this behavior intentional? If so, how should I access potentially
> overridden vals in a constructor?
>