[wellpast]

> It doesn't if the systems are well-designed sytems, comprised of loosely-coupled components

I've been going down a similar line of thought. But I went the other direction. That perhaps in "poorly designed" systems where there is lots of coupling, static typing at least gives you the "maintenance" benefit that is one of the bigger justifications that the static type apologist tends to give. You actually hear this a lot: "in large systems, static typing is a must..."

So it's interesting to me that you're going the other way and saying that actually in big, messy systems that static types may hurt you. That's not a common position.

When I walk through some of the big problems in "poorly designed" systems it almost always comes down to coupling: I can't touch one part of the system without having an effect on other parts of the system.

Interestingly, Rich Hickey criticizes the common static typer's idioms (like pattern matching and ADTs) as coupling. And he's right. What always surprises me though is that the static typer doesn't disagree -- they look at this coupling as a feature! They usually say something along the lines of "I choose static typing because if I change my Person class, then the compiler reminds me of all the places in my code that I need to go fix." What's remarkable about this is that it's not a reminder...it's an obligation that your choices plus the compiler are burdening you with: you must go update all those places in the code. This is the very definition of coupling.

There is a way to architect code such that you don't have to revisit 100 places in your architecture when some new data model decision is made/discovered. There is a way to build systems wherein you only have to touch one place in your code when some new feature or data information is needed.

[dragonwriter]

> So it's interesting to me that you're going the other way and saying that actually in big, messy systems that static types may hurt you.

In an overly-coupled late system, static typing increases the potential effect of excessive coupling in forcing changes to remote parts of the system when making what seems to be a point change. But that effect, while magnified by static typing,, is a product of coupling.

And static typing in that situation, OTOH, mitigates (as to out note static proponents are quick to point out) the chance of missing a change that will produce incorrect behavior.

On the gripping hand, reducing the excessive coupling gets to the root of the problem, while static v. dynamic is just choosing how to allocate pain that could be avoided with better architecture.

But languages are sexier than architecture.

[kbp]

> They usually say something along the lines of "I choose static typing because if I change my Person class, then the compiler reminds me of all the places in my code that I need to go fix." What's remarkable about this is that it's not a reminder...it's an obligation that your choices plus the compiler are burdening you with: you must go update all those places in the code. This is the very definition of coupling.

> There is a way to architect code such that you don't have to revisit 100 places in your architecture when some new data model decision is made/discovered. There is a way to build systems wherein you only have to touch one place in your code when some new feature or data information is needed.

The way to avoid that has nothing to do with static or dynamic typing, though. If you change a protocol then you have to change anything that relied on the old protocol if you want your program to keep working, regardless of your language's type system; in a statically typed language it will tell you where those places are, and in a dynamically typed language it's up for you to find them. If your change doesn't break a protocol that old code relied on, then you won't have to change old code. The only changes dynamic typing "saves" you from making after you break a protocol are bugfixes.

If your code is tightly coupled so that changes ripple through the entire codebase, using a language that doesn't tell you where those changes have to ripple for things to keep working won't solve that.

[benfle]

I don't see the difference between sending a Person instance and sending a map of keywords about a person. The coupling is the same.

[wellpast]

If my function only needs to know the "age", then why am I having to fill out my Person class with all the other stuff? Why, if I have facts about a Cat in hand, must I coerce it to a Person? These are hoops you're typically jumping through when you're dealing in ADTs.

[benfle]

If "age" is an important property in your system shared among different kinds of entities then you need to have an Interface or a Protocol to retrieve the age of an entity.

The same way you would create a keyword in Clojure to represent the age of an entity (e.g. ':entity/age') that can be put in a map describing a person or a cat.

In both cases you minimized the interface between your modules and you have less coupling.

[cube2222]

Not in OCaml. You can have a function like that:

let printAge object = print object.age

And it'll just check if anything passed to printAge has a field "age".

[wtetzner]

Well, in Haskell, this seems like a case where you'd want a typeclass for getting the age out of your type.

More generally, though, it seems like row-types might be a form of static typing that would fit Rich's preferred style of programming.

[tome]

That doesn't seem to describe any hoops I've ever had to jump through when using Haskell. Can you give concrete examples?

[wellpast]

I just did. Having a Person vs. Cat taxonomy. The claim is about ADTs, not Haskell. When a "name" property will do, why do we need to introduce an ADT? Why do we need to taxonomize?

[tome]

Then you can use a "HasName" typeclass. Admittedly that adds a bit of boilerplate (in one single place).

[carljv]

I think the constant replies of "Oh there's a way to deal with that." Miss the point. You should keep asking yourself, "Am I fixing a problem that didn't need to be there?" Sometimes, the answer is: No, I do want this structure, and it's worth it overall to write interfaces, etc. to add some polymorphism or dynamism to it where needed. In lots of cases, though, you're just writing stuff to accommodate the language. In lots of languages I feel like I'm fighting an internal battle between static-ness and dynamism. Start with static types or classes, then add interfaces or typeclasses, oh and overload these functions. Now make sure these other things things implement this new interface so they can participate, etc.

Sometimes it feels like a real burden for not much gain over just passing around the basic data (a name, an age) I wanted to deal with to start with. Clojure's proposition is that in many many cases, not getting fancy with the data or over-engineering your problem representation will lead to simpler programs that are easier to maintain, giving you an alternative route to safety and maintenance instead of type-checking.

[kbp]

> If my function only needs to know the "age", then why am I having to fill out my Person class with all the other stuff? Why, if I have facts about a Cat in hand, must I coerce it to a Person?

If your function only needs to know the age, then why would it take a Person or a Cat at all, instead of just accepting an age parameter? But assuming you have a reason, who says you do need to coerce anything or add any dummy data? You don't even have to go very niche to get that functionality, eg in Typescript:

    class Person {
      age: number
      constructor (age: number) { this.age = age }
    }

    class Cat {
      age: number
      constructor (age: number) { this.age = age }
    }

    const printNextAge = (thing: { age: number }) => {
      console.log(thing.age + 1)
    }

    // These all work
    printNextAge(new Person(12))
    printNextAge(new Cat(23))
    const someRandomObject = { age: 10, colour: 'green', weight: 'heavy' }
    printNextAge(someRandomObject)

    // These don't:

    const lady = { name: 'carol' }
    printNextAge(lady)
    // error TS2345: Argument of type '{ name: string; }' is not assignable to parameter of type '{ age: number; }'.
    //  Property 'age' is missing in type '{ name: string; }'.

    const caveman = { age: 'stone' }
    printNextAge(caveman)
    // error TS2345: Argument of type '{ age: string; }' is not assignable to parameter of type '{ age: number; }'.
    //  Types of property 'age' are incompatible.
    //    Type 'string' is not assignable to type 'number'.

Now, if the function takes a Person, then the reason you need to fill out the rest of the stuff is because it probably wants an entire Person, not just their age. The fact that the function can tell the compiler it needs an entire Person (and not a Cat) and have it ensure that it only gets valid Persons doesn't stop you from doing anything a non-buggy program should do, it just makes the language more expressive. Even in a wordier language with a less powerful type system like Java, which obviously isn't the gold standard for static typing (and where for some reason your function was still taking an object instead of just an age int and leaving it up to the caller to extract it), it's as simple as saying:

    interface Aged {
        int getAge();
    }

and adding 'implements Aged' to your Person and Cat classes.

[tome]

> So it's interesting to me that you're going the other way and saying that actually in big, messy systems that static types may hurt you. That's not a common position.

I didn't interpret it that way. I interpreted it as "If you have a big, messy system you can tame it into a nice, loosely couple system by adding some types".