[dkersten]

Citation needed?

Anecdotally, I've developed large projects in C++ and Java (I know, they're pretty lame static type systems -- but certainly the most popular static type systems) and also in Python and Clojure and I really haven't seen much benefit in static typing in regards to software defect rate or quality. Static typing make auto complete and refactoring tools easier, for sure, but it also slows down ease of experimentation (and writing generic code can be painful, although other static languages especially type inferred ones fare better here). I buy into Rich Hickeys view on this topic[1] and that's one reason why I like Clojure: it gets out of the way, but it provides me with the tools I need to verify or validate my data (eg on the module or application boundaries).

I've played around with languages that have fancier type systems (Haskell, various ML's, briefly ATS) and am very interested in Rust (but have yet to use it), but they haven't really provided enough benefits for the effort of describing the types.

Note that I used to be very heavily in the static typing camp and I still very much like the idea of static typing, I just don't think we have found a static type system yet that has the right balance of convenience and safety and actually catches the right kinds of errors (as described in the below talk).

I guess my point is that its not quite clear that the next generation of successful languages will all be statically typed. In fact, current trends would suggest otherwise (most of the popular languages are dynamically typed) although perhaps that depends on your definition of "successful".

[1] https://www.youtube.com/watch?v=2V1FtfBDsLU

[tome]

> I just don't think we have found a static type system yet that has the right balance of convenience and safety and actually catches the right kinds of errors (as described in the below talk).

"Please don't be an uninformed Rich Hickey talk"

<Clicks>

"Oh, it's an uninformed Rich Hickey talk"

[dkersten]

Explain?

[hasenj]

> I really haven't seen much benefit in static typing in regards to software defect rate or quality

Hold it right there. I've never seen anyone argue that static type systems prevent bugs.

I mean they do prevent silly bugs that occur from mistyping variable/property names but I've never seen anyone claim that they eliminate other classes of bugs.

The biggest benefit of static type checking is you know what all the variables are.

    def checkout_cart(customer, payment_methods, cart, session):
        # body

What the hell is customer? What is payment methods? What fields are available on these objects? What methods can you call on them? no freaking idea.

Of course, this kind of code is confusing in Java as well, but for a different reason: Java conventions encourage a kind of obtuse programming style where everything is hidden behind layers of abstractions of factories and managers, so that even when everything is typed, you're not sure what anything is doing because all the data that matters is private and so are all the methods that actually do anything useful. All you're left with is an abstract interface that can sometimes be just as bad as an untyped variable. But this is mostly a cultural problem. (I've digressed).

> Static typing make auto complete and refactoring tools easier, for sure, but it also slows down ease of experimentation

Java slows down ease of experimentation because it requires tons of boilerplate code for even the simplest tasks.

It's not the static type checking.

If anything, static type checking helps experimentation because you can change your mind quickly and the compiler will help you catch all the stupid mistakes that can occur from mismatching types or mistyping variable names. This removes a huge cognitive tax and makes programming more enjoyable. Although I will concede this is subjective.

[crdoconnor]

>Hold it right there. I've never seen anyone argue that static type systems prevent bugs.

Really? I see this every single time the subject is brought up. And, to be fair, they do catch some bugs, it's just that they do so at a cost.

>What the hell is customer? What is payment methods? What fields are available on these objects? What methods can you call on them? no freaking idea.

And, if they are all strings, how much more of an idea do you have?

Static typing does not necessarily help solve this problem - a combination of reduced scope(i.e. looser coupling), more specific variable naming and higher cohesion (e.g. having a customer object) do.

Moreover, there's a super easy way to figure out what all of those things are and figure out how you want to change it - run a behavioral test and launch a REPL when it hits that function.

At that point you can inspect customer, use autocomplete on it and even experimentally run code.

>If anything, static type checking helps experimentation because you can change your mind quickly and the compiler will help you catch all the stupid mistakes that can occur from mismatching types or mistyping variable names. This removes a huge cognitive tax and makes programming more enjoyable.

Behavioral tests perform this function equally well, if you have them.

[acdha]

> IMHO behavioral tests perform this function equally well.

I think a common pitfall in these discussions is to compare the worst case examples rather than reasonable quality codebases. I'd be far more interested in, say, time/cost to correct result metrics for a well-maintained Python codebase which has reasonable use of tests & linting (e.g. flake8) to an equivalently-proficient team using a statically typed language.

[dkersten]

If we're discussing well-maintained code, then I would expect that the public interface is documented, at least in docstrings. Then I also know what the parameters are.

[acdha]

Agreed — I'm just wondering about how to quantify the impact of various changes. A dynamic language project with no tests, etc. is going to look like a selling point for static typing but I suspect the real-world bug counts for, say, a Python project using mypy (or even flake8 + tests + coverage) is going to be a lot closer than you might think from how heated these discussions get.

[crdoconnor]

There was a study that did a line by line translation of 4 python projects to haskell and caught some bugs (between 0 and 4 per project): http://evanfarrer.blogspot.co.uk/2012/06/unit-testing-isnt-e...

I got the impression that the bugs found were either not at all serious (e.g. throwing a typeerror on malformed input instead of some other nicer kind of error) or were in areas of the code not covered by tests.

Unfortunately the author does not rate them by severity.

[hasenj]

What is behavioral test? Like, I don't understand all these weird paradigms that people come up with to deal with the deficiencies of dynamic typing.

If declaring structs is seen as costly overhead that complicates coding, tests are when more cumbersome.

[crdoconnor]

>What is behavioral test?

A behavioral test is a test that tests the behavior of a piece of software, as opposed to a test that checks types or implementation details or something else that isn't behavior.

It is perhaps not necessary to write tests like these in languages that produce code that does not have bugs. I have yet to encounter such a language.

>If declaring structs is seen as costly overhead that complicates coding, tests are when more cumbersome.

You do not write tests then?

[hasenj]

No I do not. I specially don't write unit tests.

[dkersten]

Except that static typing doesn’t help much there either (unless perhaps you’re using Frink with its units). The type doesn’t carry enough information. For example, knowing that something is an integer really doesn’t give you enough context about what that integer means or is used for. If it’s an object or strict, ok, then it helps to document, but if it’s primitive or standard collections...

Anyway, in Clojure, we now use spec to specify the shape of data that we expect, with nice descriptive namespaced keyword names. It helps in validating data entering the system, generating test data and as documentation.

[tome]

> I've never seen anyone argue that static type systems prevent bugs.

It's extremely common to claim that static typing prevents entire classes of bugs (and I agree!). Here's just one instance of such a claim I found on Google:

https://news.ycombinator.com/item?id=10934134