On 1/16/14 6:02 PM, Peter Alexander wrote:
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.
This is a good point.
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"?
To clarify:
assert(Widget.init.x == 42 && Widget.init.parent is Widget.init);
Andrei
