Null references redux

[bearophile]

Jeremie Pelletier:

> I don't remember 
> the last time I had a segfault on a null reference actually.

I have read that null deference bugs are among the most common problem in Java/C# code. I have no pointers...


> I can see what the point is with nonnull references, but I can also see 
> its not a bulletproof solution. ie "Object foo = cast(Object)null;" 
> would easily bypass the nonnull enforcement, resulting in a segfault the 
> system is trying to avoid.

That's life.


> What about function parameters, a lot of parameters are optional 
> references, which are tested and then used into functions whose 
> parameters aren't optional. It would result in a lot of casts, something 
> that could easily confuse people and easily generate segfaults.

By "optional" I think you mean "nullable" there.

Note that some of those casts can be avoided, because the nonnull nature of a reference can be implicitly inferred by the compiler:

Foo somefunction(Foo? foo) {
  if (foo is null) {
    ... // do something
  } else {
    // here foo can be implicitly converted to
    // a nonnullable reference, because the compiler
    // can infer that here foo can never be null.
    return foo;
}


> Alls I'm saying is, nonnull references would just take the issue from 
> one place to another. Like Walter said, you can put a gas mask to ignore 
> the room full of toxic gas, but that doesn't solve the gas problem in 
> itself, you're just denyinng it exists. Then someday you forget about 
> it, remove the mask, and suffocate.

No solution is perfect, so it's a matter of computing its pro and cons. It's hard to tell how much good a feature is before trying it. That's why I have half-seriously to implement nonullables in a branch of D2, test it and keep it only if it turns out to be good.

Bye,
bearophile