[ot] Scala gets a system for tracking immutability

[bearophile]

tim:
> So now D isn't the only OOP language with an immutability system:

This page:
http://old.nabble.com/Could-proved-immutable-classes-be-added-to-Scala--td14626792.html

Says:
>* Any class that extends an immutable class must be immutable

This seems true in D too:

immutable class Foo {
    int x;
    this(int xx) { this.x = xx; }
}

class Bar : Foo {
    int y;
    this(int xx, int yy) { super(xx); this.y = yy; }
}

void main() {
    auto b = new Bar(1, 2);
    b.y = 10; // Error
}

But you can omit the immutable annotation in Bar, so nowhere it's written that y too is immutable. I think this is bad, worth fixing (Bar or y have to be annotated with immutable).

Bye,
bearophile