On Friday, 17 January 2014 at 01:42:38 UTC, Andrei Alexandrescu
wrote:
Whenever a Widget is to be default-initialized, it will point
to Widget.init (i.e. it won't be null). This beautifully
extends the language because currently (with no init
definition) Widget.init is null.
Hmm, what about derived classes? How do you check for a valid
Widget given a DerivedWidget.init?
class DerivedWidget : Widget
{
static DerivedWidget init = new DerivedWidget(...);
}
bool valid(Widget w) { return w !is Widget.init; }
DerivedWidget foo;
assert(!valid(foo)); // doesn't fire, foo is valid?
The nice thing about null is that it is the bottom type, so it is
a universal sentinel value.
Also, what about interfaces? You cannot define an init for an
interface. Obviously that could just be a known and accepted
limitation of this proposal, but I'm not a huge fan of solutions
that only work in a subset of situations. Perhaps there is a
solution that I haven't thought of.
assert(x == 42 && parent is Widget.init);
Is that meant to say "x is Widget.init"?
