[james-mcelwain]

When people refer to "typing", it is almost certainly reasonable to assume they are referring to static typing, as implemented by most languages. I don't think this should be confusing.

Specs/contracts are cool but ultimately don't afford the same kind of descriptive and expressive power that a static type system does.

> static types in most languages[2] don't reduce this burden much: there isn't an alternative to thorough testing.

However, there definitely is a burden about how much testing you have to write. I generally don't want to have to test every branch of my program to make sure a string doesn't slip through where an int should be or that variables are initialized and not null, etc.

[_t0du]

I see that language parroted all the time - "With thorough enough testing a dynamic language shouldn't be a problem", and I have never understood it. Arguing to build what is essentially a build-time type checker in the form of automated tests seems twice as cumbersome for half the benefit. Instead of building tests that check each branch of a program's types, why not use a language that forbids dynamic typing? You should still have tests, but IMO tests that are just checking that a string is a string are A.) Time consuming, and B.) largely useless beyond type validation.

[smoe]

Not GP, but I have done plenty of TDD development in dynamic languages and not once have I written a test that checks whether a string is a string. You get that implicitly because others test will fail if the types don't match.

While I personally prefer certain statically typed languages over dynamic ones for new projects, In practice, for small to medium sized projects, runtime type errors is in my opinion much less of an issue as some people make it out to be. Except for null exceptions they rarely make it into production and if, are easy to track down and fix.

Interestingly, a lot of the people I have seen constantly running into type problems in say Python, are the ones coming from statically typed languages that keep insisting doing thing the way they are used to instead of embracing the duck.

[pavel_lishin]

> I see that language parroted all the time - "With thorough enough testing a dynamic language shouldn't be a problem", and I have never understood it.

"If you drive carefully enough, a car without seatbelts shouldn't be a problem!"

[alexbanks]

Exactly

[kerkeslager]

Analogies are a great way to explain things, but not so much a great way to prove things.

If you're writing software that's life and death critical like wearing a seatbelt, you should absolutely be using a strong, statically typed language, because catching errors at runtime is completely unacceptable. But incidentally, none of the proponents of static types on this thread have talked about any languages that I would actually use for this situation. Java or C-family languages certainly aren't strongly typed enough. Type systems aren't a magic bullet.

But in the vast majority of modern software, it mostly just matters that you catch and fix bugs quickly--whether you catch those bugs at compile time or runtime is usually not as critical.

[pavel_lishin]

> Analogies are a great way to explain things, but not so much a great way to prove things.

What are we proponents of static types being asked to prove?

> But in the vast majority of modern software, it mostly just matters that you catch and fix bugs quickly--whether you catch those bugs at compile time or runtime is usually not as critical.

I would argue that catching bugs at compile time, before you ship them, is vastly preferable to catching them at run time.

[kerkeslager]

> What are we proponents of static types being asked to prove?

Your arguments for why you think static types are better.

> I would argue that catching bugs at compile time, before you ship them, is vastly preferable to catching them at run time.

I would argue that you're only doing the benefit part of a cost-benefit analysis, which isn't very useful.

[kerkeslager]

> You should still have tests, but IMO tests that are just checking that a string is a string are

The correct completion to this sentence is "irrelevant.", because that's not what anyone is proposing.

The fact is, behavioral tests catch a lot of type errors even without intending to, and more to the point, if you test all the behavior you care about, then you don't care if there are type errors, because they only occur in situations where you don't care.

[jfim]

Having static type checking avoids errors caused by typos, missing match branches, and other brain fart-style mistakes. For example, in Elixir:

  f = fn
    {:ok, message} -> "It worked #{message}"
    {:eror, message} -> "There was an error #{message}"
  end

Running this

  iex(2)> f.({:ok, "yay"})
  "It worked yay"
  iex(3)> f.({:error, "oh no"})
  ** (FunctionClauseError) no function clause matching in :erl_eval."-inside-an-interpreted-fun-"/1

This kind of error isn't caught if all of the testing doesn't cover the error paths.

Contrast with Scala, where using Either (which can be Left or Right):

  def f(x: Either[String, String]) = x match {
      case Right(x) => s"It worked $x"
      case Left(x) => s"There was an error $x"
    }

If for example one forgets a branch:

  scala> def f(x: Either[String, String]) = x match {
       |     case Right(x) => s"It worked $x"
       |   }
                                          ^
         warning: match may not be exhaustive.
         It would fail on the following input: Left(_)

Or to follow the Elixir tuple pattern more closely:

  scala> sealed trait Status
       | case object Ok extends Status
       | case object Error extends Status
  trait Status
  object Ok
  object Error
  
  scala> def f2(x: (Status, String)) = x match {
       |     case (Ok, msg: String) => s"It worked $msg"
       |     case (Error, msg: String) => s"There was an error $msg"
       |   }
  def f2(x: (Status, String)): String
  
  scala> def f2(x: (Status, String)) = x match {
       |     case (Ok, msg: String) => s"It worked $msg"
       |   }
                                       ^
         warning: match may not be exhaustive.
         It would fail on the following input: (Error, _)
  def f2(x: (Status, String)): String

The typo also gives an obvious type error:

  scala> def f2(x: (Status, String)) = x match {
       |     case (Ok, msg: String) => s"It worked $msg"
       |     case (Eror, msg: String) => s"There was an error $msg"
       |   }
             case (Eror, msg: String) => s"There was an error $msg"
                   ^
  On line 3: error: not found: value Eror

Caveat: still learning Elixir and my Scala is rusty, so there might be better ways of doing the above. :)

[pavel_lishin]

> if you test all the behavior you care about, then you don't care if there are type errors, because they only occur in situations where you don't care.

If I test all the situations I care about, the one situation I thought I didn't care about is going to fuck me in production.

[kerkeslager]

If you test all the situations you care about and statically type check, the one situation you thought you didn't care about and that wasn't caught by the type checker is going to fuck you in production.

It's not useful to talk about a binary "bugs versus no bugs", because "no bugs" isn't plausible in most codebases.

It's also not useful to talk about "more bugs versus fewer bugs" because that's only part of the picture: the other parts of the picture are how much development effort was necessary to achieve the level of bugs you have, and whether the number of bugs you have, and when you have them, is acceptable.

If it's a life or death application where any bugs at runtime are unacceptable, then of course we want static types, but static types aren't enough: I'd also want a theorem prover, fuzzer, a large number of human testers, and a bunch of other things that require way too much effort to be useful in an average software project.

The vast majority of software projects, runtime bugs are acceptable as long as they don't lose data, cause downtime, or expose private information. If you catch these bugs during unit testing instead of 30 seconds earlier at compile time, that's fine. Static types might catch a few more bugs, but it is very much not in evidence that the level of effort involved is lower than equivalent unit testing in situations where reliability requirements are typical.

[_t0du]

My personal real life experience with Ruby developers disagrees with you, but I accept that I could just have experienced a set of developers that weren't very good at testing.

[peferron]

Trust your experience.

It's impossible to defeat the claim that "with good tests you don't need static type checking", since every counter-example can be dismissed by arguing that better developers would have covered that test case.

I can claim just the same that "with correct code you don't need tests", and dismiss every counter-example by arguing that better developers wouldn't have made that mistake.

Obviously we know that developers sometimes make mistakes, and sometimes these mistakes are in the tests themselves. So trust your experience regarding how this all works out.

[_t0du]

Yeah. You formulated my opinion much more elegantly than I could've - in my experience it's always the "Well if the tests didn't catch this, we just aren't testing enough." Which in my experience is a losing strategy, you'll never test "enough" in languages like Ruby.

In my experience this idea always brings a strawman, "Well in statically typed languages you still have to test", which is obviously true. But the type of tests and the content of the tests is very different.

[kerkeslager]

> Yeah. You formulated my opinion much more elegantly than I could've - in my experience it's always the "Well if the tests didn't catch this, we just aren't testing enough." Which in my experience is a losing strategy, you'll never test "enough" in languages like Ruby.

Maybe someone is saying that, but I didn't say that.

My question isn't whether you can test enough to catch all bugs. My question is whether time spent wrangling types gets you more value than time spent writing tests.

> But the type of tests and the content of the tests is very different.

Are they? How so?

Again, unit tests of the form `assert isinstance(foo, type)` are an antipattern--that's not what I'm proposing.

[bryanrasmussen]

type errors are generally the lowest common denominator error, thus tests that catch higher level errors will also catch whatever typing error is related to the actual error you are testing for.

Not to say I haven't had benefits from catching type errors but generally not as great as those I have from having an automated GUI test running.

[JohnBooty]

    However, there definitely is a burden about how much
    testing you have to write. I generally don't want to 
    have to test every branch of my program to make sure 
    a string doesn't slip through where an int should be 
    or that variables are initialized and not null, etc.

This has not been my experience!

I've been writing Ruby full-time for about six years (including one of the largest Rails apps in the world) and I don't find this particular aspect of Ruby to be a problem whatsoever relative to statically-typed language.

Ruby is famously easy to write tests for. Creating mocks in a dynamic language is such a breeze. There are plenty of problems with Ruby but an increased test suite burden is NOT one of them. "Confident Ruby" by Avdi Grimm is a great read in this vein; not about testing specifically but writing confident Ruby code in general.

Part of it is simple, human-friendly code hygiene. Give your arguments descriptive names and use keyword params when possible. If you have a method:

    foo(user_name:, height_cm:)

...then you'd really have to be asleep at the wheel to write something like this elsewhere in your code:

    foo(user_name: 157, height_cm: "Smith")

And so you don't need to write your code or your tests with any real extra level of paranoia. If somebody does pass a string to `height_cm:` it will return a runtime exception, just like it should.

Of course, I do get type errors all the time in Ruby, but that's when I'm parsing JSON or something and that's generally not something static typing's gonna help you with anyway.

Now... there ARE places where I miss strong typing in Ruby.

One, I miss having extremely intelligent IDEs like you can have with Java or C#. I absolutely loved Visual Studio and Resharper in the C# world. The amount of reasoning it can do about your code and the assistance it can give you is absolutely bonkers.

Two, obviously, there is a price in runtime execution speed and RAM usage to be paid for dynamic typing. I don't find raw execution speed to be much of a bottleneck in a Ruby app because Postgres/Redis/etc are doing all my heavy lifting anyway. RAM usage and app startup times with large applications is more of a real-world issue.

[phtrivier]

My counterpoints would be:

First, if you're writing any kind of big code, than somewhere, in your code base, someone else is writing a code where the user name is spelled `username`. Or `user`. You don't have to be "asleep at the wheel" to not remember, or not know, which is which. So you're going to type the wrong one (not necessarily on purpose), and you'll get a runtime error. Not that bad, sure, but you'll get it.

Also, at some point, you'll realize that a string is not the ideal way to represent a user name [1], and some of the functions that deal with users are going to start returning a Struct %User{first_name: ..., middle_name: ....}. Or will it be a Map %{"first_name" => ...} ? And surely you're going to track all the calls of `foo` to fix them. And all the calls of all the calls of `foo`, because, who knows ? And suddenly you're doing the mental job of a static type checker. Surely you're not "asleep at the wheel" anymore, because you're doing the work of the wheel by manipulating the gears by hand.

Bottom line: I'll gladly admit that I'm too old and stupid to do that anymore. I had typechecking in the 90s. Give it back.

[1]: https://www.kalzumeus.com/2010/06/17/falsehoods-programmers-...

[JohnBooty]

Thank you for the thoughtful reply!

    So you're going to type the wrong one (not 
    necessarily on purpose), and you'll get a runtime 
    error. Not that bad, sure, but you'll get it.

I agree with your facts but not your conclusion here. This certainly happens, but this is trivially caught by your integration tests.

Now, it's certainly true that in a static language, your compiler would catch this for you. In a decent IDE it would be pointed out to you while you type.

However, static or dynamic, you're going to be writing tests anyway, so I can't view this as some sort of increased burden when it comes to writing tests.

    Also, at some point, you'll realize that a string is not the 
    ideal way to represent a user name [1]

I have loved that article since it came out! It's one of those things I saved as a PDF just in case the original goes offline someday.

I don't think your examples are realistic, at all, though.

1. If you replace `User#first_name` and `User#last_name` with `User#name` (which returns a `Name` object) your test suite is going to blow up all over the place every time you call the deleted `User#first_name` or `User#last_name` methods anyway. And now you have a list of places where you need to fix your code.

2. But, what if you update the internal structure of `Name` over time? Some of the above applies. But also callers of `Name` shouldn't know too much about `Name` anyway - it should be providing some kind of `Name#display_name` or whatever function that handles all of the complexity and returns a dang string anyway.

Everything I've written here presumes the existence of a test suite, of course. Which of course takes time to write and maintain. But any nontrivial project needs one anyway regardless of language or type paradigm, right?

    Bottom line: I'll gladly admit that I'm too old and 
    stupid to do that anymore. I had typechecking in 
    the 90s. Give it back.

Absolutely the same here. But, I seem to miss it in different places than you.

I miss static types when I'm writing code. I want my IDE to tell me the types and type signatures when I type, and draw a little squiggly line under my code when I get it wrong. In Ruby, I wind up having 10 different files open at a time in my text editor so I can see what various methods are expecting.

This is mitigated somewhat by simply bashing out a lot of my code in irb/pry directly, since pry's `show-source` can at least tell me stuff.

[theonething]

> I wind up having 10 different files open at a time in my text editor so I can see what various methods are expecting.

Huh, I thought this was normal. Not everyone does this?

[phtrivier]

No. Something like "intellisense" has existed for decades. It relies on the static type system to "guess" what functions make sense in a given context. You Ctrl-Space your way to writing the code , ans get Brain cycles back to actually think about stuff.

[JohnBooty]

Yes. This is the scenario in which I truly miss a good old-fashioned static type system and a big ol' intelligent IDE. Specifically, because of what you said: it frees up brain cycles for me to think about the real problems.

My highly subjective belief and experience is that Ruby and its ecosystem has enough other perks to make up for this loss. But, I definitely accept others might feel otherwise.

[ianamartin]

>> When people refer to "typing", it is almost certainly reasonable to assume they are referring to static typing, as implemented by most languages.

Really? You're going to go with "most languages implement static typing"?

That seems like a bold statement.

[james-mcelwain]

I'm not making a claim about all languages, I'm talking about languages that support any kind of extensible type validation, whether statically or at runtime.

[kerkeslager]

If you're willing to include dynamic types, then I really don't know what you're even talking about. Literally no language I know of doesn't do validation at runtime: assembly does type validation at runtime (try dividing by zero).

[mapcars]

>Specs/contracts are cool but ultimately don't afford the same kind of descriptive and expressive power that a static type system does.

What exactly dialyzer type checking lacks compared to static type systems?

[kerkeslager]

> When people refer to "typing", it is almost certainly reasonable to assume they are referring to static typing, as implemented by most languages.

I don't think that's a reasonable assumption at all. Even if, as you assert, the average person doesn't understand that types exist in dynamically-typed languages, I don't think that means I have to conform to common misconceptions.

> Specs/contracts are cool but ultimately don't afford the same kind of descriptive and expressive power that a static type system does.

True, but not what I was talking about.

Could you explain what descriptive and expressive power is missing here?

    class Square(Rectangle):
        def __init__(self, side_length):
            self.side_length = side_length

        @property
        def height(self):
            return self.side_length

        @property
        def width(self):
            return self.side_length

[uryga]

> Could you explain what descriptive and expressive power is missing here?

tldr: i haven't seen a runtime typechecker that handles generics and function types in a satisfactory manner.

i've used various Python libraries for runtime type-checking (based on `typing` annotations) like `typeguard`. and they work okay for simple types, but suck for anything involving generics and function types. checking if something is a `List[int]` every time it's passed as a parameter is too expensive, because you have to go through the whole list (and you're out of luck if it's an Iterator[int] - can't traverse that without exhausting it). runtime typecheckers don't have enough information to check if something is a valid `CustomList[int]`. and they have no way of checking if e.g. a function (passed as a parameter) is actually a `str -> int`, at best you'll find out when you call it.

and runtime checkers, at least the ones i've used, often end up requiring more annotations than i'd have to write in a type-inferred language. it might be possible to work around that to some degree, but I think that's a fundamental limitation – unlike a static checker, they only have info about code that already ran. so you'll have to annotate code like this:

  f xs = cons 'a' xs

because a runtime checker can't "look into the future" and tell that based on the usage of `cons`, the only sensible type for `xs` is List[Char], so `f` must be of type `List[Char] -> List[Char]`.

[kerkeslager]

> i've used various Python libraries for runtime type-checking (based on `typing` annotations) like `typeguard`.

Let's just stop right there, since it's immediately clear you aren't answering the question I asked. You're talking about type checking, not descriptive and expressive power.

The topic is whether dynamic types are suitable for domain modeling, not whether dynamic types provide static type checking. We all agree that dynamic types don't provide static type checking.

[uryga]

alright, just to clarify, from the comment that introduced expressive power into the discussion:

> Specs/contracts are cool but ultimately don't afford the same kind of descriptive and expressive power that a static type system does.

i understand that as "the ability to describe/enforce the domain's rules".

now, i guess i made a bit of leap, jumping to runtime typechecking. my thinking was that while modelling your domain, you might want to specify that e.g. `width` and `height` must at least be numeric (i know i would!); `typeguard` et al are a concise way of doing that in Python, but have their limitations. so static types can be more "expressive" if the tools i mentioned (generics and function types) are useful for describing your domain model, which i often find to be the case.

looks like i missed the mark there; but in that case, i'm not sure what point you're making with that Square class. it's hard to say what's missing (or not) because there's not a lot there.

[kerkeslager]

Well, let's be clear here: the code already expresses that height and width are numeric. You read the code and knew they were numeric; QED. In fact, if you think a bit deeper, you probably know a few more things about the type of those variables: they're positive, for example.

And if you're using a mainstream statically typed programming language, you probably aren't actually going to express that it's a numeric using the type system. 90% of the time someone will just throw `int` on there and call it a day, and that type expresses a bunch of lies about the height and width: it says it can be negative, and it says it can't be a decimal, and it says it can't be greater than the INT_MAX of you machine. `unsigned long` and `double` are both a little better, but are still expressing a bunch of lies. And that's if you are in a more modern language: in C, for example, you're telling the compiler that it's totally cool to add the side_length to a char* and (depending on you settings) not even warn about it.

So I have to ask, where exactly is this expressive power you're talking about? You're only gaining the ability to express things to the compiler, not humans, and it doesn't actually give you the ability to express what you want to express to the compiler. You've eliminated the narrow class of bugs where:

1. The code passes in a non-numeric.

2. The bug occurs on a path not traversed in normal testing.

And you've done this at the cost of your code not being able to handle a lot of the numeric values you might want to be able to handle.

[uryga]

honestly, if this is going to be about static vs dynamic typing in general, i'm going to peace out because this argument has been rehashed about a million times. and we seem to be talking past each other anyway

i just wanted to make a point about how checking types at runtime doesn't mesh well with generics and functions, so it's always going to be limited on that axis. and perhaps there's a dynamically typed nirvana where you just handle that differently, but it's a problem i personally had

[edit: removed unnecessary snarkiness]

[james-mcelwain]

> the average person doesn't understand that types exist in dynamically-typed languages

Again, this is needlessly uncharitable as to what people mean when they talk about type systems, which is obviously about the capabilities of defining new types for program analysis, not that the runtime has an internal conception of types.

> Could you explain what descriptive and expressive power is missing here?

Sure! Looking at this, I have no idea what the size of side_length is, whether it's possible for it to be negative, or whether it's possible it to be null.

Of course, unless you're writing purely square based software, most domains are more complex than this. But I still think it's pretty helpful to know the properties of the parameters being passed to build your square are!

[kerkeslager]

> > the average person doesn't understand that types exist in dynamically-typed languages

> Again, this is needlessly uncharitable as to what people mean when they talk about type systems, which is obviously about the capabilities of defining new types for program analysis, not that the runtime has an internal conception of types.

There is nothing "internal" about the example I gave. That's valid Python code that creates a type.

My definition (which happens to be the actual definition of the word) charitably assumes that people know dynamic type systems exist, so I don't think you can really accuse me of being uncharitable. If anything I'm being too charitable, as evidenced by this conversation.

> Sure! Looking at this, I have no idea what the size of side_length is, whether it's possible for it to be negative, or whether it's possible it to be null.

> Of course, unless you're writing purely square based software, most domains are more complex than this. But I still think it's pretty helpful to know the properties of the parameters being passed to build your square are!

Do you really not know whether side_length can be negative or null? Or are you just saying that to be argumentative? If we're pretending we don't know obvious things, why not just go all the way and pretend we don't know that side_length is a number?

As for not knowing the size: why would you want to have to know the size? The fact that this square will work with any numeric type is a feature, not a bug.

Now, consider this (disclaimer: my C++ is rusty, and I didn't syntax check this):

    class Square: Rectangle {
      private:
        double sideLength;
      public:
        Square(double sideLength) {
          this.sideLength = sideLength;
        }
    }

Let's evaluate this based on your complaints about the Python example:

1. The size of sideLength. Well, yes, this example does tell you what size it is. Which is rather annoying, since now you have to cast if you want to pass in an integer, and you might overflow your bounds. This is an annoyance, not a feature.[1]

2. We know that sideLength can't be negative because we know what squares are. The type doesn't enforce that. You could enforce that by using unsigned int, but then you can't handle decimals. And in either case, you can't use very very large numbers. I haven't worked in a static typed codebase which has an unsigned BigDecimal type, have you?[1]

3. We know that sideLength can't be null because we know what squares are. The type system technically also tells us that, but the type system telling us what we already know isn't particularly useful.

[1] Haskell's numeric type can actually handle this much more cleanly than C++, as I mentioned upthread. But in typical Haskell, you'd probably just let the types be implicit in a lot of cases.