[Jach]

Null isn't that bad -- or rather, the concept of a missing value. Certain languages handle null better than others, but even then, it seems like the more costly mistake has been the accumulation of made-up data to satisfy non-null requirements.[0] More costly for non-programmers who have to deal with the programmers' lazy insistence that not knowing a value for some data in their system is forbidden, anyway.

In any case I think the modern fashion of trying to eliminate null from PLs won't matter much in the effort to replace C, whereas something like a mandatory GC is an instant no-go (though Java at least was very successful at sparing the world a lot of C++). OTOH a language that makes more kinds of formal verification possible (beyond just type theory proofs) might one day replace C and have null-analysis as a subfeature too.

[0] http://john.freml.in/billion-dollar-mistake

[electrograv]

I think the author of that blog post fundamentally misunderstands the point: The damage of nullable pointers is not that they are nullable, but that compilers allow you to write code everywhere that assumes they’re not null (in fact, this is the only possible way to code, when the language cannot express the notion of a non-nullable reference!)

For example, most older languages with “the billion dollar mistake” have no complaint whatsoever when your write “object.method();” where it’s unknown at this scope whether “object” is null or not.

The fact that such code compiles is the billion dollar mistake; not the fact that the pointer is nullable.

I don’t care if you want to write nullable references everywhere, or whatever else you prefer or your application demands. That’s fine, so long as:

1. Non-nullable reference types must exist.

2. Nullable references types must exist as statically distinct from #1.

3. The compiler must not let you write code that assumes a nullable reference is not null, unless you check via a control flow statement first.

Now to take a step back, the principle behind this certainly applies beyond just nullability (if that was the point you were trying to make): Generally, dynamic, untyped invalidation states are dangerous/bad, while statically typed invalidation states are ideal. And yes, this does include bad states internal to a non-null reference, just as much as to a null reference.

Sum types are the key to being able to statically declare what range of values a function may return (or accept), and ensure at compile time that these different cases are all accounted for. If you aren’t aware of how elegantly sum types solve this, you should look into it — and I suspect it will be quickly clear why nullable references are useless, outdated, and harmful.

But at the very least, we’ve solved the pain of null dereference — and virtually without compromise. So, it’s irresponsible or ignorant IMO to create a new language that doesn’t include this solution in its core.

[gameswithgo]

It doesn't seem like you are familiar with how option types get rid of null. You don't have to make up data to satisfy things not being null. You set them none, and the language either forces, or encourages usually, you to always check if the option is none or some.

[Jach]

I use Option in Java quite a bit because I'm real sick of NPEs and cascading null checks in all-or-nothing flows. I would have preferred Java starting with something like Kotlin's approach where T is T not T|nil. You and the sibling might be missing the point of the post I linked, I think. It can be convenient to have formal assistance via e.g. the type checker that a function taking a non-null String returns a non-null Person with a non-null FirstName and LastName. But in the zeal to be rid of null to make programmers' lives a bit easier, when faced with a name that doesn't compose into 2 parts, someone has to decide what to do about that and who needs to care down the line. You can make up data ("FNU" as in the blog), set a convention (empty string), throw an exception, or declare either the whole Person structure Optional or at least certain fields. If you use a dynamic late-binding language you may have other options. Whatever you do, it ought to be consistent or robustly handled where the references interact with your DB, your processing programs, and your data displays. Finally when these references escape your system, as lots of real world data does, they necessarily escape any static criteria you once had on them, thus it's important to consider those third party systems have to live with your choice. Null is a convenient choice, not something to be villified so casually.