I think the nullable reference type system in c# is a perfectly workable compromise for languages that had nullability from the very beginning. Once a code base uses them fully, most null-related bugs are gone. And it’s far from an unwieldy bolt-on.
So T? doesn't compose, while Option<T> does, which I'd consider a big difference.
However, without a builtin option type, duck-typing, or a pleasant way of converting the types, Option<T> may become a hassle (especially when different dependencies ship their own). And as T? is shipped with the language this is probably why it is used when the composability is not required.
P.S.: In C# T? even neatly composes.
return obj?.a?.b
if (obj != null && obj.a != null) {
return obj.a.b
} else return null;Does nesting Option's really has practical use or does it quickly become confusing?
In your example, Option<Option<T>> return type doesn't tell me by itself that this differentiates between a missing file or a missing setting. I would need to get this information from somewhere else.
In other words, nested optionals might not be very readable, but they're a necessary product of having a highly modular, reusable toolkit, and you can always massage them into more informative, domain-specific types at whatever point that becomes appropriate.
The thing is that nullable covers majority of cases and is quicker to read and write (Foo? vs Option<Foo>). Doing a?.b?.c is also more elegant than anything equivalent using an Option type.
Is there any languages that successfully combines both, nullable '?' syntax and an Option type?
Which leads to a bit of an argument - nesting gives poor ergonomics, while collapsing impacts the ability to write generic code.
Rust has dozens of helper methods for option - like map, map_or, map_or_else, and so on. When you’re starting out, it’s quite hard to find what you want in the morass of options. And many of the helper functions take a closure, which messes up your ability to do control flow (return, break, continue) from the containing function. In Swift, like typescript, I found the syntax sugar around options to be much easier to learn. Eg obj?.a?.b rather than checks docs obj.and_then(|o| o.a).and_then(|a| a.b).
“If let” in rust helps. (Similar to guard let in Swift) Ie, you can write if let Some(x) = x { … }. But you still can’t combine that with other conditions in the if statement - which drives me nuts.
myobj.dothing(x).otherthing(y)
Of course the Rumsfeld Matrix further breaks down the three different types of unknowns.
https://en.wikipedia.org/wiki/There_are_unknown_unknowns
>"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones." -Donald Rumsfeld
1) Known knowns: These are the things we know that we know. They represent the clear, confirmed knowledge that can be easily communicated and utilized in decision-making.
2) Known unknowns: These are the things we know we do not know. This category acknowledges the presence of uncertainties or gaps in our knowledge that are recognized and can be specifically identified.
3) Unknown unknowns: These are the things we do not know we do not know. This category represents unforeseen challenges and surprises, indicating a deeper level of ignorance where we are unaware of our lack of knowledge.
And Microsoft COM hinges on the IUnknown interface.
https://en.wikipedia.org/wiki/Tony_Hoare#Research_and_career
>Speaking at a software conference in 2009, Tony Hoare apologized for inventing the null reference:
>"I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years." -Tony Hoare
https://news.ycombinator.com/item?id=19568378
>"My favorite is always the Billion-Dollar Mistake of having null in the language. And since JavaScript has both null and undefined, it's the Two-Billion-Dollar Mistake." -Anders Hejlsberg
>"It is by far the most problematic part of language design. And it's a single value that -- ha ha ha ha -- that if only that wasn't there, imagine all the problems we wouldn't have, right? If type systems were designed that way. And some type systems are, and some type systems are getting there, but boy, trying to retrofit that on top of a type system that has null in the first place is quite an undertaking." -Anders Hejlsberg
Eg they can't distinguish between one or two layers of nullable. Or between null and an optional null.
(In eg Rust syntax between `Option<Option<MyType>>` vs `Option<MyType>`. Or `()` vs `Option<()>`, where `()` would be how you spell `null` in Rust.)
Using tags is simpler and cleaner.