[goatlover]

Alan Kay's argument against static typing was it was too limited and didn't capture the domain logic of the sort of types you actually use at a higher level. So you leave it up to the objects to figure out how to handle messages. Given Ruby is a kind of spiritual ancestor of Smalltalk.

[Barrin92]

the problem is that nobody listened to Alan Kay and writes dynamic code the way they'd write static code but without the types.

I always liked Rich Hickey's point, that you should program on the inside the way you program on the outside. Over the wire you don't rely on types and make sure the entire internet is in type check harmony, it's on you to verify what you get, and that was what Alan Kay thought objects should do.

That's why I always find these complaints a bit puzzling. Yes in a dynamic language like Ruby, Python, Clojure, Smalltalk you can't impose global meaning, but you're not supposed to. If you have to edit countless of existing code just because some sender changed that's an indication you've ignored the principle of letting the recipient interpret the message. It shouldn't matter what someone else puts in a map, only what you take out of it, same way you don't care if the contents of the post truck change as long as your package is in it.

[nradov]

That's a terrible solution because then you need a bunch of extra parsing and validation code in every recipient object. This becomes impractical once the code base grows to a certain size and ultimately defeats any possible benefit that might have initially been gained with dynamic typing.

[Barrin92]

>then you need a bunch of extra parsing and validation code in every recipient object.

that's not a big deal, when we exchange generic information across networks we parse information all the time, in most use cases that's not an expensive operation. The gain is that this results in proper encapsulation, because the flipside of imposing meaning globally is that your entire codebase is one entangled ball, and as you scale a complex system, that tends to cost you more and more.

In the case of the OP where a program "breaks" and has to be recompiled every time some signature propagates through the entire system that is significant cost. Again if you think of a large scale computer network as an analog to a program, what costs more, parsing an input or rebooting and editing the entire system every time we add a field somewhere to a data structure, most consumers of that data don't care about?

this is how we got micro-services, which are nothing else but ways to introduce late binding and dynamism into static environments.

[akoboldfrying]

> when we exchange generic information across networks we parse information all the time

The goal is to do this parsing exactly once, at the system boundary, and thereafter keep the already-parsed data in a box that has "This has already been parsed and we know it's correct" written on the outside, so that nothing internal needs to worry about that again. And the absolute best kind of box is a type, because it's pretty easy to enforce that the parser function is the only piece of code in the entire system that can create a value of that type, and as soon as you do this, that entire class of problems goes away.

This idea is of using types whose instances can only be created by parser functions is known as Parse, Don't Validate, and while it's possible and useful to apply the general idea in a dynamically typed language, you only get the "We know at compile time that this problem cannot exist" guarantee if you use types.

[9rx]

> The goal is to do this parsing exactly once, at the system boundary

You are only parsing once at the system boundary, but under the dynamic model every receiver is its own system boundary. Like the earlier comment pointed out, micro services emerged to provide a way to hack Kay's actor model onto languages that don't offer the dynamicism natively. Yes, you are only parsing once in each service, but ultimately you are still parsing many times when you look at the entire program as a whole. "Parse, don't validate" doesn't really change anything.

[akoboldfrying]

> but under the dynamic model every receiver is its own system boundary

I'm not claiming that it can't be done that way, I'm claiming that it's better not to do it that way.

You could achieve security by hiring a separate guard to stand outside each room in your office building, but it's cheaper and just as secure to hire a single guard to stand outside the entrance to the building.

>micro services emerged to provide a way to hack Kay's actor model onto languages that don't offer the dynamicism natively

I think microservices emerged for a different reason: to make more efficient use of hardware at scale. (A monolith that does everything is in every way easier to work with.) One downside of microservices is the much-increased system boundary size they imply -- this hole in the type system forces a lot more parsing and makes it harder to reason about the effects of local changes.