function modifiesValField(struct: {val: number}) {
struct.val = 0;
}
But I do get your point - although type systems have gotten much less annoying, its not like they're perfect.
This is true. But also I've noticed many less experienced TS devs end up writing types that are too specific and not utilizing structural typing enough. So e.g. writing some type and demanding a function accept it, when that function only actually needs one or two properties from it. Instead that function can inline or localize the part of the type it needs, and the original type can be unaware its ever being used by some other function.
And the other thing is trying to leverage the type system too much. For my style, if the types aren't making things easier to read, write, and maintain, they should be loosened and / or duplicated. I blame a lot of libraries here, it should never be puzzling to figure out how to type something so a function accepts it, yet that comes up quite often; I end up diving through these nested and overly DRY types trying to find what the heck even is this thing? That's crazy. If you need to cmd+click more than once or twice to understand what a type is, its way too abstracted.
That's a pretty big if, though. You will never catch me in my typed backyard, writing tests that say: if typeof(arg) =! string then return error("Not a string!")
An additional problem of course is that solutions that assume extra work from people, tend to be brittle ones (also thinking about "manual backups" here) aka. those tests will end not being written at all.
And, if you do not write tests, there is a bunch of other problems that will surface, which will not be caught by the compiler itself. What I'm saying is static types give you feedback loop:
write code -> make the project compile -> fix bugs
while the dynamic ones give you:
write code -> fix bugs (including type ones).
Obviously, YMMV. For me it works. And to be honest, from my experience nothing is more brittle than a type hierarchy designed early in project lifetime and then fixed repeatedly until it "works", but again - to each their own.
This is basically the entire reason I am so excited about Zig.
Edit: it's also the reason I have a love/hate relationship with typescript. Typescript almost lets you do this if you try really hard, but at the end of the day it's not designed to truly test your code and requires you to "cheat" in order to make the types properly describe the situation; every time you "cheat" in order to get a more expressive type (whether that's looser or narrower), you would have been better off writing a test instead.
On the other hand, sometimes I feel like it has a lot to do with test writing. I feel people enjoy static typing, because you can get a feedback loop catching certain things without writing any tests. If you do write tests, all the type errors get caught pretty immediately anyway, so I just don't see the benefit.
Personally, the biggest advantage of dynamic typing for me is the ability to skip formalities for a time. If I want a function that can modify any struct with field "val" in (by, let's say, setting it to zero), I can - and I don't have to do multiple definitions, I don't have to define an interface. Just a function and I am done. If I want to skip error handling for now and only code the happy path, I can - and my program will work (and crash on error, but in some cases it's ok).
As the projects get more complex and require higher safety guarantees, static typing helps in ensuring nothing got broken - but nothing beats dynamic typing for prototyping.