> I don't have numbers on that, though I think a sibling comment did refer to some.
I've read that paper in the past and it doesn't actually answer most of the questions I asked above. It only says that X bug existed in some prior git commit. Maybe the dev caught that bug and fixed it before the PR with the commit was merged. Maybe it was caught in code review. Maybe it was theoretically possible within the function, but not within the actual program's use of that function. Maybe the time spent catching those bugs was less than the time it would take to add types.
> they allow me to not write some of the unit tests I'd written otherwise
A `typeof` assertion or similar is hardly more work and continues to function once the TS types have been stripped. If you expect to interact with the outside world, then you must test against unexpected types. If not, then good docs are still better (see below). Meanwhile, in every real-world TS project I've worked on, you wind up with tons of "template soup" where devs spend tons of time trying to find out which variant makes the type checker happy (or just giving up and slipping in an `any` type)
> Yes, I still have to write documentation, but just iterating the types is not documentation?
I have a function that takes a string and returns a boolean. What does it do?
It's likely that I can pass it any string, but there's a strong possibility that the function can't handle any random string. Does that boolean mean it's a test, that something was successful, or something else? What about side effects?
By the time you're done documenting this, when someone glances at the docs, they'll probably not worry very much about the types because they'll be obvious. Why write up a bunch of complex types when a simple, human-readable doc string does types and so much more?
> I've read that paper in the past and it doesn't actually answer most of the questions I asked above.
OK, well I still don't have the numbers, so we have nothing better than intuition to go on regarding whether it saves time/improves quality or not.
> A `typeof` assertion or similar is hardly more work and continues to function once the TS types have been stripped.
Yes, and if a typeof assertion is enough, than you don't need any additional syntax in TypeScript either. But a `typeof val === "object"` doesn't tell me a whole lot though.
> If you expect to interact with the outside world, then you must test against unexpected types.
Agreed. That said, with TypeScript, you only have to do it once, at the point where you interact with the outside world. Once I've verified that e.g. my API response contains all the properties I expect, then I can pass it on to any other function in my code safely. Whereas without TypeScript, I have to be aware at the points where I access those properties that the original source of that value might have been the outside world, and to explicitly verify that it looks as expected. (Or alternatively, I need to still verify the object at the boundary, but have to manually know what properties of it are accessed in the rest of my codebase.)
> Meanwhile, in every real-world TS project I've worked on, you wind up with tons of "template soup" where devs spend tons of time trying to find out which variant makes the type checker happy (or just giving up and slipping in an `any` type)
Yes, I've seen that happen to. I will not argue that you don't have to learn TypeScript, and that if you do not (want to) put in the effort (or are unable) to do that, it might be counter-productive. In fact, I advised another team in my company to move off of TypeScript for that very reason.
> By the time you're done documenting this, when someone glances at the docs, they'll probably not worry very much about the types because they'll be obvious. Why write up a bunch of complex types when a simple, human-readable doc string does types and so much more?
Yes, type annotations are not a replacement for documentation. They help your tooling help you. So the reason to write up a bunch of complex types (well, preferably simple types most of the time, of course) is that your tooling can help catch mistakes early - I'm not working off of documentation most of the time. I read it once, refer back to it every now and again, but more than that would be a massive waste of time. My memory is a major asset in being able to quickly type out a bunch of code, but my tooling helps me by removing the need to memorise some things.
I've read that paper in the past and it doesn't actually answer most of the questions I asked above. It only says that X bug existed in some prior git commit. Maybe the dev caught that bug and fixed it before the PR with the commit was merged. Maybe it was caught in code review. Maybe it was theoretically possible within the function, but not within the actual program's use of that function. Maybe the time spent catching those bugs was less than the time it would take to add types.
> they allow me to not write some of the unit tests I'd written otherwise
A `typeof` assertion or similar is hardly more work and continues to function once the TS types have been stripped. If you expect to interact with the outside world, then you must test against unexpected types. If not, then good docs are still better (see below). Meanwhile, in every real-world TS project I've worked on, you wind up with tons of "template soup" where devs spend tons of time trying to find out which variant makes the type checker happy (or just giving up and slipping in an `any` type)
> Yes, I still have to write documentation, but just iterating the types is not documentation?
I have a function that takes a string and returns a boolean. What does it do?
It's likely that I can pass it any string, but there's a strong possibility that the function can't handle any random string. Does that boolean mean it's a test, that something was successful, or something else? What about side effects?
By the time you're done documenting this, when someone glances at the docs, they'll probably not worry very much about the types because they'll be obvious. Why write up a bunch of complex types when a simple, human-readable doc string does types and so much more?