alt Hacker NewsI like to think about how many problems a feature solves to judge whether it's "worth it". I believe that the Sum types solve enough different problems that they're worth it, whereas nullability solves only one problem (the C-style or Java-style null object) the Sum types can solve that with Option<T> and also provide error handling with Result<T, Err> and control flow with ControlFlow<Continue, Break> among others so that's already a better deal.
Nullability is a good retro-fit, like Java's type erased generics, or the DSL technology to cram a reasonable short-distance network protocol onto the existing copper lines for telephones. But in the same way that you probably wouldn't start with type erased generics, or build a new city with copper telephone cables, nullability isn't worth it for a new language IMO.
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Erased generics give parametricity, which most PL people think is fairly important. See https://en.wikipedia.org/wiki/Parametricity or https://www.cl.cam.ac.uk/teaching/1617/L28/parametricity.pdf
I'm an advocate for "both".
- `Option<T>` and `Result<T,E>` at core;
- `?T` and `T!E` as type declaration syntax that desugars to them;
- and `.?` and `.!` operators so chains like `foo()?.bar()!.baz()` can be written and all the relevant possible return branches are inserted without a fuss.
Having `Option` and `Result` be simply normal types (and not special-casing "nullable") has benefits that are... obvious, I'd say. They're just _normal_. Not being special cases is great. Then, having syntactic sugars to make the very, _very_ common cases be easy to describe is just a huge win that makes correct typing more accessible to many more people by simply minimizing keystrokes.
The type declaration sugar is perhaps merely nice to have, but I think it really does change the way the average programmer is willing to write. The chaining operators, though... I would say I borderline can't live without those, anymore.
Chaining operators can change the SLOC count of some functions by as much as... say, 75%, if we consider a language like Go with it's infamous "if err not nil" clause that is mandated to spread across three lines.