[recursivedoubts]

My general take (and w/ the caveat that every system is different) is as follows:

- procedural code to enter into the system (and perhaps that's all you need)

- object oriented code for domain modeling

- functional code for data structure transformations & some light custom control flow implementation (but not too much)

I like the imperative shell, functional core pattern quite a bit, and focusing on data structures is great advice as well. The anti-OO trend in the industry has been richly earned by the OO architecture astronauts[1], but the idea of gathering a data structure and the operations on that data structure in a single place, with data hiding, is a good one, particularly for domain modeling.

In general I think we are maturing as an industry, recognizing that various approaches have their strengths and weaknesses and a good software engineer can mix and match them when building a successful software project.

There is no silver bullet. If only someone had told us that years ago!

[1] - https://www.joelonsoftware.com/2001/04/21/dont-let-architect...

[bunderbunder]

OO code for domain modeling might be, to date, the single greatest source of disillusionment in my career.

There are absolutely use cases where it works very well. GUI toolkits come to mind. But for general line-of-business domain modeling, I keep noticing two big mismatches between the OO paradigm and the problem at hand. First and foremost, allowing subtyping into your business domain model is a trap. The problem is that your business rules are subject to change, you likely have limited or even no control over how they change, and the people who do get to make those decisions don't know and don't care about the Liskov Substitution Principle. In short, using one of the headline features of OOP for business domain modeling exposes you to outsize risk of being forced to start doing it wrong, regardless of your intentions or skill level. (Incidentally, this phenomenon is just a specific example of premature abstraction being the root of all evil.)

And then, second, dynamic dispatch makes it harder for newcomers to figure out the business logic by reading the code. It creates a bit of a catch-22 situation where figuring out which methods will run when - an essential part of understanding how the code behaves - almost requires already knowing how the code works. Not actually, of course, but reading unfamiliar code that uses dynamic dispatch is and advanced skill, and nobody enjoys it. Also, this problem can easily be mitigated with documentation. But that solution is unsatisfying. Just using procedural code and banging out whatever boilerplate you need to get things working using static dispatch creates less additional work than what it takes to write and maintain satisfying documentation for an object-oriented codebase, and comes with the added advantage that it cannot fall out of sync with what the code actually does.

Incidentally, Donald Knuth made a similar observation in his interview in the book Coders at Work. He expressed dissatisfaction with OOP on the grounds that, for the purposes of maintainability, he found code reuse to be less valuable than modifiability and readability.

[sqeaky]

This is a strong argument against inheritance, but that isn't everything about OOP. Just one well supported advanced abstraction (That I would also argue should be rarely used.)

I would argue that just having strong type system and bundling methods with data gets you the vast majority of the usefulness of OOP. Liskov, Open/Closed, Message Passing, and other theoretical abstractions be damned.

EDIT - Where are the good places to use inheritance?

There are only a few I can think.

One is when you are trying to create a system that inverts dependencies by allowing a plugin system or follows some sort of nuanced workflow that others might want to "hook into". But that isn't the only way to do that, maybe other ways would be better like passing in functors.

Another situation I have seen recently is when creating a kind of data or messages that differ only by type and maybe a few small pieces of behavior and they are all known up front.

[marcosdumay]

> I would argue that just having strong type system and bundling methods with data gets you the vast majority of the usefulness of OOP.

Yes, a module system brings almost all of the advantages of OOP. The one remaining is structure abstraction (things like interfaces on Java derived languages, or type classes on Haskell derived ones).

But well, none of those are even typically associated with OOP. The OOP languages just have those features, like they have variables too.

[josephg]

Yep. Rust has all of these features (modules, structs with associated methods and type classes (traits)). But nobody thinks of it as an OO language. In fact, I’ve heard that many people struggle with rust if they’ve come from a heavily OO language like Java. You have to structure your code a little differently if you don’t have classes.

Modula apparently had many of these features too - and that predated what we now think of as object oriented programming. The good parts of OOP aren’t OOP.

[moth-fuzz]

> One is when you are trying to create a system that inverts dependencies by allowing a plugin system or follows some sort of nuanced workflow that others might want to "hook into".

I’m fairly certain that’s the use case of inheritance - at least in the Simula tradition. Classes as a means of lifetime management, moving parts that have well defined steps of operation (methods), and interchangeable parts (subtypes) which you can more or less slot into the larger system (polymorphism).

It’s easier to think about classes not as nouns, but as verbs over time (or rather, bounded by time): at a specific moment in the assembly line, call this particular method, at another moment, call that other method…

Object oriented programming in the Simula tradition I would even go as far as to say is just best practices in structured/procedural programming taken to their logical extremes.

[jancsika]

> Classes as a means of lifetime management

Wrt plugin systems: at least as the class level, are classes really a means of lifetime management in practice?

IIRC, audio plugin APIs follow the shell command pattern of memory management for loading new classes-- the user dynamically loads a library into a running instance of an application, and there it stays until the application exits.

And even if plugin systems as implemented are actually unloading classes, the user is almost always just restarting the app to make sure it took. :)

Edit: clarification

[recursivedoubts]

Agree 100%: static typing (for code completion) + method/data bundling is the major win in OO, and it rarely gets talked about for whatever reason.

It's unfortunate that inheritance became such a major focus of practical OO languages. Would love to see a composition-first OO language. Might have its own problems, but would at least be interesting.

[1propionyl]

Go, Rust, Zig, etc all support static typing and method/data bundling without any explicit language support for implementation inheritance (interface inheritance in general and especially when structural rather than nominal is not nearly as much of an issue and doesn't create strict tree hierarchies).

Rust has support for variance and subtupint so perhaps it's not as pure of an example, but it's pretty heavily restricted.

Zig's support for method/data bundling being used for "objects" isn't even first class so I wouldn't call it OO (object-oriented) so much as object-orientation-capable with less fuss than if one wanted to build their own objects system in C.

[sqeaky]

Even in C++ the last time I thought I might need inheritance I made a simple class/struct with a few members that were `std::function` instances. Instead of needing inheritance this worked and I managed to keep type safety checks on all function return and parameter types. Once upon a time this would have been weird function pointers and `void*` with dangerous casts. Last month when I did it, there were just lambdas passed to typesafe constructors.

[mjevans]

Go's first class support for typed return tuples and Interfaces is a lovely replacement for inheritance (E.G. an Interface of type blah supports this signature). They function as an API contract, if a given class implements the requirements of the Interface, it can be cast to and used as that anywhere which accepts that interface.

[bunderbunder]

It's not unfortunate happenstance, it's by definition.

Dynamic dispatch is the defining feature of object-oriented programming. In dynamically typed languages such as Smalltalk, you can get there with duck typing. But a statically typed language needs a statically typed mechanism for dynamic dispatch, and that requires some way of saying, "Y is a particular kind of X, so all members of X are also in Y." Which is - again by definition - inheritance.

You could remove - or refuse to use - the inheritance (or, equivalently for some purposes, duck typing). But that would also prevent the use of dynamic dispatch, so what you're doing would bee be procedural programming, not OOP, even if you're using an object-oriented language to do it.

[randomdata]

> Dynamic dispatch is the defining feature of object-oriented programming.

Message passing is the defining feature of object-oriented programming. Dynamic dispatch can be achieved using message passing, but message passing is more than dynamic dispatch.

Ultimately, static typing is incongruent with object-oriented programming. Messages are able to be invented at runtime, so it is impossible to apply types statically. At best you can have an Objective-C-like situation where you can statically type the non-OO parts of the language, while still allowing the messages to evade the type system.

[jerf]

Whether you'd call "composition-first" is probably asking for a big argument about what "composition first" really means, but Go is certainly a language that syntactically privileges a particular type of composition over inheritance. It doesn't even have syntax for inheritance, and frankly even manually implementing it is rather a pain (best I've ever done requires you to pass the "object" as a separate parameter to every method call... and, yes, I said that correctly, to every method call).

I'm not ready to try to stake a position on the top of some "composition first" hill because the syntactic composition it supports is not something I use all the time. It's an occasional convenience more than a fundamental primitive in the language, the way inheritance is in inheritance-based languages. Most of the composition is just done through methods that happen to use in composed-in values, but it is generally not particularly supported by syntax.

[cjblomqvist]

Typescript and it's structural typing my be what you're looking for.

[bigstrat2003]

Inheritance is just plain a great way to model a lot of relationships, in my experience, because a lot of things are most easily thought of as "x is a kind of y". I am perennially baffled that people shit on inheritance so much, because I think it's incredibly useful. I find myself often missing inheritance when working in Rust, for example.

[bccdee]

Implementation inheritance often leads to code that is just awful to read. If class C extends class B and class B extends class A, then to find out what `new C().foo()` actually does, you need to read through the whole C-B-A hierarchy, bottom to top. If `A.foo()` calls `this.bar()`, you have to start again, from the bottom of the hierarchy. With an inheritance hierarchy of depth n, every method call could be going any of n different places. With an interface, there's a single level of indirection. With composition, the code simply tells you what happens next.

If class A and class B both implement interface X, and B wants to borrow code from A, it should just call A's methods—ideally, static methods, but B can keep an instance of A if it wants. Explicit is better than implicit.

Also, I dislike ontological statements like "x is a kind of y." What does that mean? Typically, it's a claim about behaviour: "x offers method w and satisfies invariant v". But the actual blueprint here is an interface, (w,v)—not another object y. The waters get even muddier when we start talking about "is-a" vs "has-a" relationships. It feels like OOP is trying to unhelpfully distance us from what's actually going on with our code. Under the hood, inheritance is no more than syntactic sugar for composition. I think that OOP's focus on the ontological philosophy of inheritance is the reason why it led to so much bad AbstractObserverStrategyFactory-style code.

[pjc50]

> dynamic dispatch makes it harder for newcomers to figure out the business logic by reading the code

This is definitely a potential problem, but I note that you can also get into this mess without OO in any language that lets you put a (reference to) function in a variable. Or, god help you, operator overloading.

[bruce343434]

Operator overloading isn't to blame.

If I overload shift-left `<<` for a completely different concept such as "piping", that's my mistake. That's like writing a normal function or method and calling it `foo()` when it has nothing to do with the concept of fooing.

That said, unless you are writing a math library or some container, there's not many good uses for operator overloading.

[pjc50]

> If I overload shift-left `<<` for a completely different concept such as "piping", that's my mistake.

Yours and C++'s.

[frogulis]

I think the main difference between the two is, as someone reading and debugging the code, will probably eventually check even those methods that I assume I know roughly what they do. In contrast, I may not even think to check an overloaded operator unless I _already know_ that it's overloaded.

Maybe a good analogous method would be an overloaded `.ToString()` in C# that has side effects or returns the full text of the Magna Carta or something.

[bunderbunder]

Custom operators of any kind are definitely a problem for learners. I think people just fixate on overloading because that's the only kind of operator customization available in the most popular languages.

The particular problem is that search engines tend to have terrible support for searching for arbitrary sequences of non-alphabetic characters.

[fenomas]

I'm not a big thinker on such things, but my general rule is that subtyping is okay only for implementation details.

I.e. it's okay for ConsoleLogger to be a subtype of Logger, but PaidUser probably shouldn't be a subtype of User.

[green_dee]

So interfaces > modelling

ConsoleLogger is a Logger because they share a method (log), PaidUser and User can have some common things, but I don't think it's only in the way it behaves, but also in the way you contact/use them

[beryilma]

But, in a way, OO modeling and design was invented to solve the mess that "banging out" procedural code created in the first place.

You have to model your business domain in software one way or another anyway. Why should it be bad to try to be more methodical about it using OO methods? We do it with relational databases all the time where tables are pretty similar to objects.

[nanomonkey]

OO and Relational databases really don't mix well, so much that there are wikipedia articles on the subject [0].

ORMs create some of the worst SQL table layouts that I've ever seen, not to mention they generally cause tons of N+1 query problems.

[0] https://en.wikipedia.org/wiki/Object%E2%80%93relational_impe...

[arendjr]

I actually have nothing against objects and methods, but that’s a very limited subset of OO. I prefer to use algebraic data types for domain modeling, and giving them methods is totally fine too. But I do prefer them to be immutable in most cases, which is also quite counterintuitive from an OO perspective.

[j45]

The real world definitely isn't OO all the time.

Maybe more functional and event based.

The oscillation between the two as what's in favour is also humorous.

The right thing for the right need for the present and near future, especially the newer the codebase, and the greater the need to learn, is often the way to consider pursuit.

[temporarely]

> The real world definitely isn't

Ironically, (ime/o!h;) it turns out this the "root of evil" plaguing abstraction: thinking that software architecture must map to "the real world".

[epgui]

I think you have it backwards.

Software exists in the real world, and is used to solve real world problem. In building software we inevitably invent or use abstractions to represent or effect real world things. Abstractions that make it easier to do this are good, abstractions that make it harder to do this are just getting in the way.

[josephg]

> In building software we inevitably invent or use abstractions to represent or effect real world things.

Ehhh. Most abstractions I’ve written aren’t abstractions over the real world. They’re abstractions over low level machinery of a computer or program. (Eg there’s no HTTP request and response, DB connection or network socket outside of computer software).

The real world isn’t object oriented. It’s just a bunch of atoms moving around. You can describe physical reality as a bunch of objects that interact via ownership and method calls, but there’s nothing natural about that. OO is no better of a way to describe the real world than actors & message passing, or state & events.

Software that models “the real world” usually describes users, money, addresses and things like that. But none of those things are made out of atoms. There is no money molecule. Money is not on the periodic table. They’re all just another form of abstraction - one that happens to exist outside the software world, that we can capture in part in a database table.

Interesting abstractions are all invented ideas. Some are useful. Some are elegant to express and use in OO code, and some are not.

[temporarely]

1 - (Application) System exist in the real world, not software. Software exists in machines.

2 - Computing is used to solve real world problem.

3 - "In building software we inevitably invent or use abstractions to represent or effect real world things." Here is the problem where we part company.

4 - Abstractions that inform computing systems are indeed useful.

[edit+ps]

self disclosure: I've reached 'architectural orbit' numerous times in my career. 30 years later, I am sharing a subtle point. Effective software models cutout attributes of real world elements of the problem domain. All attempt to "model the world" end in tears.

[epgui]

This reads like nonsense to me, so I can only assume the disagreement is semantic.

[j45]

For me, software and tech that is for someone, exists to work for people, who are end users.

End users and customers don't exist to serve at the leisure and pleasure of software and it's creators.

Making people work harder than they need to operate software is selfish.

DevOps and DevEx is important, but if no one uses it with those being great, the Customer and their experience are often lost and never gained.

Learning to model something flexible enough for absorbing and quickly implementing the early customer feedback that is relevant is critical to boring things like retention.

Helping customers earn enough to eat every month, helps the tool makers earn enough to eat every month.

[anymouse123456]

FWIW - OO has the same (or more) problems in GUI toolkits.

[dgb23]

> object oriented code for domain modeling

I'm not sure about that.

If we're talking about IT (information processing in general), then the domain model is just data representing facts and should probably be treated as that, and not some metaphorical simulation of the world.

I've come up with a pretty useful test for when to apply OO:

When you need to model a _computational unit_[0] in terms of _operational semantics_, then use OO.

[0] Decidedly _not_ a simulation of a metaphor for the "real world".

---

Examples:

A resizable buffer: You want operations like adding, removing, preemptively resizing etc. on a buffer. It's useless to think of the internal bookkeeping of a buffer that is represented in its data structure when you use it.

A database object: It wraps a driver, a connection pool etc. From the outside you want to configure it at the start, then you want to interact with it via operations.

A HTTP server: You send messages to it via HTTP methods, you don't care about it's internal state, but only about your current representation of it (HATEOAS) and what you can do with it.

A memory allocator: The name gives away that you can _do_ things with it. You first choose the allocator that fits your needs, but then you _operate_ on it via alloc/free etc.

---

Some of us wince when we hear "OO", because it has been an overused paradigm. Some advocates of OO have been telling us that it is somehow total (similar to FP advocates) and people have been pushing back on this for a while now.

When applied to information processing especially, it becomes ridiculous, complex and distracting. I call this "Kindergarten OO": You to write code as if you explain the problem to a child via metaphors.

Computational objects however arise naturally and are very obvious. I don't care if those are encoded as classes, with closures or if we syntactically pretend as if they aren't objects. They are still objects.

[epgui]

If you think OOP is particularly well-suited to domain modelling, you should try the FP approach to domain modelling.

You will never be able to unsee the complexity inherent to OOP.

[brabel]

You can try the FP approach today in most languages that are not even FP:

* Rust * Kotlin * Dart * Java

Yep, even Java. Check this out: https://blog.jdriven.com/2021/10/sealed-classes/

[jprete]

Do you happen to have a link to an example or explanation?

[arendjr]

The keyword to search for is algebraic data types, which are common in functional languages, but for instance Rust also has them.

Here is an example comparing C# with F#, where the latter also algebraic data types: https://blog.ploeh.dk/2016/11/28/easy-domain-modelling-with-...

[neonsunset]

The syntax has improved quite substantially since 2016 for pattern matching at C#'s end, and it's very easy to model ADTs with records (and the experience of using them even before that was decent with methods accepting lambdas).

Today, you write it in a similar way you would write a match in Rust.

[nequo]

How do you represent sum types in C# today? Can enum members hold records as data, or do you do it differently?

[rapnie]

Domain Modeling Made Functional [0] by Scott Wlaschin

[0] https://www.youtube.com/watch?v=2JB1_e5wZmU

[epgui]

The other commenter is not technically wrong to point at “algebraic data types”, but I don’t think that answer is helpful at all. It’s like saying the answer to data modelling is tuples.

I would instead recommend searching for “functional programming and domain driven design”.

[mejutoco]

> but the idea of gathering a data structure and the operations on that data structure in a single place, with data hiding, is a good one, particularly for domain modeling.

One can do this in a module without OOP.

The idea of mixing data and behaviour/state (OOP) instead of keeping data structure and functions transforming those (functional) is IMO the biggest mistake of OOP, together with using inheritance.

I believe making part of the program data instead of code (and thus, empty of bugs) is such a big advantage. Already lisp was talking about it. Mixing data with behaviour, without a clear delimitation creates a tight-coupled implementation full of implicit assumptions. Outside the class things are clean, but inside they ossify, and grow in complexity. Pure functions with data in data out are such a big improvement in clarity when possible.

[sqeaky]

I hadn't thought about it explicitly like this before, and I think I agree. My more nebulous thought process was something like:

1. Try to solve the problem purely functionally.

2. If that failed because of data issue, model the data with objects and simple operations in an OOP style or well thought collection of arrays (game devs answer to OOP causing memory and caching problems, but the end result programming is similar to OOP thought process)

3. If that is can't happen because some external restriction is impose use the minimal amount of procedural logic to solve the problem and round off as many sharp corners as is practical until it is unlikely any on the team gets cut.

Logically that is very close to inversion of thought process and ordering of operations to what you suggested. But I think we would recognize each others attempts to pick a design paradigm in code.

Now I want to think about this more. Is there some underlying principle here? Is this some kind of underlying principle? Where do domain specific languages fit in? Do other paradigms fit in? What are the bounds of this pattern, where does this process fail?

[voidhorse]

Look, I'm going to catch flak for this but at the end of the day the main problem is that Java and C++, the most popular OOP languages, are just bad programming languages.

There are OOP languages out there, most of them older than Java and C++, that actually provide a much better set of knobs and handles for writing sane OO programs.

Java is finally getting a bit better thanks to a lot of market pressure and good ideas from Kotlin. C++ will probably be a mess forever.

[kingofthehill98]

That's the strategy I always take when designing a system. Funny that I never thought about it before, I think most PHP developers will relate to that aswell.

- Procedural single point entrance into the system (network -> public/index.php, cli -> bin/console)

- OOP core for business logic, heavily borrowed (copied) from Java OOP model

- Functional code inside classes/methods whenever possible (callables/closures, array_map/filter/reduce/walk, illuminate/collections, etc.)

[gwbas1c]

> These things might be good architectures, they will certainly benefit the developers that use them, but they are not, I repeat, not, a good substitute for the messiah riding his white ass into Jerusalem, or world peace. No, Microsoft, computers are not suddenly going to start reading our minds and doing what we want automatically just because everyone in the world has to have a Passport account.

Priceless.

[Dwedit]

When you write a procedure that has to maintain an internal state between calls, changing it into a class makes sense. As for the name, you change the verb (write) into a noun (writer), and you now have a name for the class.

C# will silently create hidden closure classes for you when you use lambdas or yield.

[arendjr]

Just know that if you do this, you’re injecting statefulness in the center of wherever it was this procedure was being used. If your entire system already has statefulness everywhere, nobody will bet an eye. But if you want to have any chance at creating a functional core or island, it’s the opposite of what you should be doing.

[alex-robbins]

When you write a procedure that has to maintain an internal state between calls, stopping what you're doing and switching to functional programming makes sense.

[NomDePlum]

James Gosling, who I'd consider the father of one of the most popular OO languages gave this advice:

"You should avoid implementation inheritance whenever possible"

My early days of Java where largely building unmaintainable inheritance trees into my code and then regretting it. This quote gave me comfort that it wasn't really that good an idea.

Decent discussion on inheritance Vs composition also found here: https://en.m.wikipedia.org/wiki/Composition_over_inheritance