[sirwhinesalot]

I agree "high cohesion, loose coupling" is a good architectural property to strive for, but OOP is terrible at it and there's no reason to use it for this.

Trying to achieve "high cohesion, loose coupling" in OOP has led to the creation of (supposedly) best practice recommendations like the SOLID principles, and the development of monstrosities like dependency injection frameworks.

If OOP was actually good at "high cohesion, loose coupling", you wouldn't need them.

[KayEss]

I think this is looking at what OOP has become (as implemented by systems and programming languages that don't care a wit about what OO was meant to be) rather than what Alan Kay described.

If you think about something like a web server as an object, it has arbitrarily high cohesion and arbitrarily low coupling. You can only communicate to it through messages (HTTP); binding happens at the point in time that the message arrives (notwithstanding that this may be cached in all sorts of interesting ways in the implementation of any given server); and the web server is fully encapsulated (security flaws notwithstanding).

I think it's perfectly reasonable to argue that much of what gets called OOP doesn't deliver on the promise, but then it doesn't deliver on the premise either, and I think these are inextricably linked.

[sirwhinesalot]

The Alan Kay variant of OOP is superior in this regard, and I'd argue the Erlang variant even more so (Actors are just asynchronous objects).

But both of them are still suboptimal because they allow objects to instantiate one another and to directly communicate with whomever they come in contact with. That creates strong coupling and you have to "fight the paradigm" to avoid it.

Other engineering domains have this figured out: components can only send and receive data through ports, they are never aware of their siblings. Only a component at a higher level of abstraction can decide how the ports of lower level components connect to one another. That completely eliminates coupling.

(You can of course replicate this type of architecture with OOP, but you can also replicate it with any turing complete paradigm, that's neither here nor there)

[mccoyb]

Linda and Syndicate figured this out - it’s just that most engineers are not programming language designers or researchers, and most researchers are not designing robust scalable language implementations.

[sirwhinesalot]

It's crazy to me that Linda came out 40 years ago. I think our field is completely blind to what was achieved in the past.

Smalltalk is to me the most obvious case where people somehow don't realize we had a fully live environment, where the entire IDE (or really the whole operating system) could have open heart surgery done on it while it was running, in the late 1970s!

And that's a language that is at least somewhat in the public consciousness, languages like Linda? Nobody knows them. Synchronous languages like Lustre and Esterel? Some engineers know them (and pay good money for them), but not software engineers.

[KayEss]

I have fond memories of bricking my Smalltalk environment several times trying to get instance behaviour working :-)

[ElevenLathe]

Thank you for pointing me to Linda -- fascinating and my mind is popping with fun projects related to this model. It actually seems quite spiritually similar to "Bank Python" (https://calpaterson.com/bank-python.html), but more elegant.

[sph]

Linda: https://en.wikipedia.org/wiki/Linda_(coordination_language)

By Syndicate you mean syndicated actors?

[mccoyb]

Exactly, the work of Tony Garnock-Jones: https://syndicate-lang.org/

[Folcon]

When you say other engineering domains have figured this out, can you give a more specific example?

[sirwhinesalot]

Yes, for example if you are doing any sort of mechatronic systems engineering (cars, planes, rockets, etc.), you're typically using tools like Simcenter Amesim or Modelica or Simulink/Stateflow to digitally prototype the system.

These tools are all oriented around blocks with ports. They receive data on their input ports and emit data on their output ports. They do not know where that data is coming from nor where it is going. They cannot instantiate other blocks.

To create a new block you either create a primitive one (described directly in terms of differential equations, since these are physical simulations, or as actual code, be it C or MATLAB or whatever else), or you connect blocks together to form a larger block.

This creates a strict hierarchy, connections between blocks can only happen at the same level of abstraction. You can just rip out a component and replace it with another with the same ports, or with multiple components each filling in part of the job, or you can plop another component in the middle that's only used to process the data inbound and redirect it somewhere else.

This makes coupling extremely loose by design. The paradigm enforces it.

[saint-evan]

'in->func()->out' work cleanly for physical engineering domains because blocks of computations (or functions) have no memory basically. There's no DB and there's usually no global state in the way you'd mean with classes. I've observed that when you work on complex software, you could play by the ear to enforce 'high cohesion and loose coupling' up to the point to where you've now got a data store holding system state. Based on what I've worked on, this system state is actually user data and then some derivative of the system's own interaction on this user data, both of which are necessary for the 'continuity of system runtime'. For example, working with redis as the primary data store, I extracted different types of redis calls for specific keys, (like set [specific_key], get [specific key], etc.) into functions, then I put these functions into a StateStore class so I can simply call StateStore.get_user_data() or StateStore.set_user_data() etc from any module across the entire system. From first principles, this is great modularity and high cohesion but it's very tight coupling around a single module i.e. StateStore. Any change in that module means I'd have to find all references for that updated function and cross check for any contract violations. It's difficult for me to see how software can purely be 'High Cohesion and Loose Coupling' regardless of paradigm or architectural pattern. There's always gonna be an unavoidable and inevitable principle violation that's simple a result of a large complex system actually doing many little things that come together to actually do one big thing. The software itself, no matter how complex, IS the blackbox where data goes in and something comes out but that's the user perspective not ours as the programmer. I think the idea I'm trying to hint at is that software cannot have every module independent of every other one. That's impossible. If nothing depended on anything else, the system wouldn't do anything. Rather than have every module know redis keys, States tore actually concentrates coupling into one place, which is exactly what high cohesion tries to accomplish. I think that's the idea I'm chasing.

[sirwhinesalot]

It's not really true that components in physical engineering domains have no memory. The behavior of many physical components can only be described with access to a recent history. Other components, specially controllers, are typically state machines (which obviously have state).

But it is true that there will always be parts of a software system that are highly coupled. I'm not even sure if that's even a problem, unless the coupling is also highly tangled (meaning the connections are coming from too many places).

But if you want to decrease coupling between parts of a system, OOP by itself is not particularly good at it. Even something like an Entity Component System is usually less coupled than most OOP codebases because while each System is heavily coupled to the components they do work on, the Systems are usually fully independent from one another and easily replaceable.

[socketcluster]

There are definitely cases where you could have a module with distinct responsibilities; so you can definitely get high cohesion and loose coupling without OOP, that's true, but there are cases where you may want to:

- Control the timing of when a module is activated (instantiated).

- Have multiple instances of a module with variations in functionality where those variations are not a concern to the parent module/instance.

For me, this is when OOP becomes most useful. If I can write some code once and later use it to create any number of independent instances with the same functionality which can clean up after themselves, this is generally a lot more maintainable than having one module to keep track of all the different states in an array and micromanaging (for example) the rendering and cleanup work associated with multiple distinct pieces of state.

[sirwhinesalot]

To be clear I'm not arguing against objects here, I don't disagree with anything you wrote. I'm only arguing against the somewhat commonly held idea that OOP helps with loose coupling.

Interfaces (a feature of OOP) can be used to decrease coupling, but the paradigm itself doesn't really provide any assistance in regards to coupling.

The default is for objects to directly instantiate other concrete objects and to be able to directly communicate with any object they at any point come in contact with. That is strong coupling, by default.

You have to do extra work to get looser coupling. Smalltalk style OO is much better (regarding coupling) because you don't have explicit interfaces, you can always replace an object with another. You can also query all live objects of a certain type and replace all of them with a proxy if you so wish. Way better.

But you can go even further in regards to loosening coupling. You can have objects communicate through a tuplespace (Linda), you can have objects receive and send messages only through ports, you can have objects send a message to their implicit parent who is then responsible for redirecting it.

Mainstream OOP is a very poor paradigm full of issues that gets mogged by everything. Composition-over-inheritance is an admission of defeat for a paradigm that lacks native delegation support (good on Kotlin for realising this).

It even gets mogged by languages like Haskell that introduced the more loosely coupled idea of typeclasses, which were inherited by Rust (traits), Swift (protocols), Go (interfaces, not to be confused with declaration-time interfaces as in Java).

We dug a suboptimal hole and stuck our head in there for 50 years.

[socketcluster]

I think OOP helps to build loosely coupled systems but it doesn't protect you from tight coupling. You have to know what you're doing.

I think OOP languages made some pragmatic decisions. Sometimes a feature which is harmful 95% of the time could be genuinely useful and safe 5% of the time... Some languages like Haskell might choose to not allow that feature at all and force the developer to find another approach which is almost as effective for that 5% of cases; that's fair enough. It's a different philosophy.

I feel like that about passing mutable objects by reference. I find it harmful most of the time but there are rare cases were it's convenient and beneficial. I've worked on open source projects were I wanted the user to be able to use the software with any database so my function accepted a database adapter as an argument.

I could have achieved a similar goal in another way but I would have had to sacrifice separation of concerns slightly. I wanted the ability to substitute any database but also wanted the component to be responsible for the persistence and recovery of its own state as this was within its responsibilities. Also this was the only violation in the entire codebase so I deemed it acceptable. It didn't pose any problems at all in practice.

[sirwhinesalot]

I think dogma is far worse than "tight coupling" or introducing mutation or even inheritance when it is the simplest and most direct solution to a problem. People get too hung up on the "ideal" way to do things.

I can criticize a paradigm while also using it anywhere and everywhere it benefits me ;)

[Kinrany]

I dislike OOP as much as the next HN commenter, but dependency injection tools are good in principle. OOP just uses them much more and for bad reasons.

[sirwhinesalot]

Dependency Injection frameworks are a workaround for limitations of the paradigm, much like Design Patterns also are. They're necessary (by a very stretched definition of necessary) because people want to do certain things and the paradigm is fighting them.

Some part of the code wants to do logging. The paradigm-native solution is to just instantiate a logger object directly, but that's not really what you want to happen, because there are application-level concerns as to where those logging messages should go.

So instead of a direct new, you create a Logger interface (extra work), then use the Factory pattern (extra work) to hide the concrete logger objects that get instantiated. Ok, but now you are still creating multiple independent loggers, which will trample on each other.

So you employ the Singleton pattern (extra work), but now you can't use different loggers for different parts of the codebase.

Ok, let's instead have the application instantiate the proper loggers, and then thread them through method arguments as needed (extra work).

But now passing all those loggers around is super annoying and extremely noisy, so you create a framework that can inject them where they are needed.

Great, now you have a whole framework just to pass some logger objects around. The framework is not the problem per se, it exists for a reason, the problem is that someone felt the need for it. And it is a massive pile of complexity that is NOT worth it.

[Kinrany]

Ignoring the singleton for now, because I don't quite see the need.

What's the alternative? Which part of this is actually caused by OOP? If you want to isolate IO, which you should, then you need to inject things that do IO and you need to specify a contract for them. And then it's nice to instantiate things or call functions without explicitly instantiating the whole tree of their dependencies.

[sirwhinesalot]

There are various ways to solve the problem (if you consider it a problem, I personally don't, there's no need for things to be this extremely decoupled, but for the sake of argument):

1) Allow objects to send messages to an implicit "parent" object, which supports "doesNotUnderstand" ala Smalltalk and that by default also forwards to the implicit parent. That means you can implement "log(...)" at the right point in the abstraction without manually passing a logger around.

2) Use algebraic effects, no need to handle this with OOP. A function requests the "log" effect and a handler defined in a higher level scope takes care of implementing log.

3) Have a language with an implicit context parameter that allows putting arbitrary things in it (closest would be Odin but Odin has a fixed set of operations in the context). Because it is implicit in the calling convention methods can be oblivious to it.

4) You separate the concerns: logging is the act of recording some information. Where that information is ultimately sent or stored is a separate concern. This is the more functional view of the problem. If you follow a "model-view-update" approach like the so called "Elm Architecture", logging is just another task produced by the view function, it doesn't need any special handling.

It's not that this is a "problem" of OOP, it is that OOP doesn't give you any tools for tackling this problem. That is why dependency injection frameworks exist. Some other paradigms and non-OOP architectures don't have any trouble with it. You can also replicate those architectures in an OOP language, but that's still "contorting the paradigm" rather than it helping or guiding you towards a clean solution.

Personally I think a global singleton logger is perfectly reasonable, it is other people (the ones using DI frameworks) that think otherwise ;)

[bluGill]

OOP isn't why they are used. OOP may enable injection more than others, but it is not encouraged. Bad programmers and bad architects is why it is overused not OOP. Keep the blame in the right place.