| > Testing is a cost. It is more code to write, more code to maintain. I'm not saying you write tests to protect against NPEs. I'm saying that you write tests to ensure correctness of your code, and as a side-effect NPEs are flushed out of your code. This is my theory explaining why NPEs are not a timesink for me. > They guarantee the correctness of the invariants of the Red Black Tree, and they easily replace hundreds of lines of test code which give no guarantee. Code with mathematical invariants seem like such a niche area, though. The average type of test that I write is "ensure your service calls service X first checking for values in a cache; ensure that it can handle cache unavailability, service X unavailability, cache timeout, service X timeout". Maybe you could figure out a way to encode that in a typesystem, but I'd wager that it wouldn't be as readable as the equivalent written as a test. > Scala shuns null - and only has it for Java interop. All Scala developers I've discussed this with program as if null did not exist, and never use it to signify lack of a value. That's exactly right. Languages with nulls, and mutable shared state are perfectly reasonable to use if programmers do the right thing by convention. > When "arguing with a compiler"... I misspoke. I was thinking of the learning process, not the process of writing code. Although my current focus is backend systems, I have worked across the spectrum in the past. I've worked (not including languages I dabble at home) in JS (for browser UIs), Java (for Android UIs and servers), Obj-C (for iOS UIs), Python (for servers and scripts), Scala (for servers), Ruby (for servers), and C++ (for servers). These languages represent a wide spectrum on the dynamic to static spectrum. I don't find myself writing much safer code when I go from JS to C++. The same for a shift from Ruby to Scala. The same for Python to Java. These shifts are relatively large on the type-system spectrum, as they go from dynamically typed languages to statically typed ones. You claim that a significantly smaller shift, removing nullability from a language would be a big deal for reliability. That doesn't seem likely to me. |
You never know when you have enough coverage to rule out NPEs or any other bug. And to get confidence about lack of NPEs you want to have coverage of all lines involving dereferences, which means you need near 100% test coverage to have a reasonable level of confidence. With Haskell, I can be reasonably confident about my code with very little tests.
> but I'd wager that it wouldn't be as readable as the equivalent written as a test.
Generally types are far more concise and guarantee more than tests. I find 5 lines of types more readable than dozens or hundreds of lines of tests.
> That's exactly right. Languages with nulls, and mutable shared state are perfectly reasonable to use if programmers do the right thing by convention
I think Scala users will generally disagree with you. They'd prefer it if null was ruled out in the language itself. That said, Go convention is to use nulls, not shun them.
> I don't find myself writing much safer code when I go from JS to C++. ... Ruby to Scala ...
Your code is much safer simply by construction, so I am not sure what you mean here.
> You claim that a significantly smaller shift, removing nullability from a language would be a big deal for reliability. That doesn't seem likely to me
Hitting type errors at runtime, null dereference crashes in Java and "NoneType has no attribute `...`" in Python is pretty common IME.
I do think non-nullability aids reliability, but that having sum types, proper pattern matching and parametric polymorphism aids it even more. And Go lacks all of these.