Jonathan M Davis:
// x is a nullable class reference
if (x == null) {
...
} else {
// here the type system sees x as not null.
}
??? What does it matter if the type system knows whether a
pointer is null
unless it's trying to warn you about dereferencing null?
In the else branch the state of the type of x is not-null, so as
example in the else branch you are allowed to call a function
that only accept not null references, with the x variable.
Not-nulls integrated in the type system makes sure you have well
initialized variables in the class constructors in presence of
inheritance and other complexities.
It also statically requires you to test for null before
deferencing a nullable class reference, ans so on.
Those are the fruits that a good not-null implementation gives
you. You can't do all this with the NotNull toy. NotNull solves
only the easy part of the whole problem, and it's a small part.
Actually, it is. I said "that I'm aware of."
Right :-)
Bye,
bearophile
