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One of the most memorable eye-opening moments in my (admittedly fractured) education was when when my software engineering professor listed the 3 fundamental tenets of OO—inheritance, encapsulation, and polymorphism—and then asked us which one was optional.

Ever since then I've been on an anti-inheritance kick, although for the last several years it's polymorphed into an anti-OO kick.

Anyway, I suspect most readers here have heard the idea that inheritance should be used in limited circumstances (or not at all), but I wonder what proportion of college students get that message today.

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I agree with "anti-inheritance" as a general guideline, but its adherents have to recognize the significant practical upsides of inheritance in many situations.

Imagine you have an interface with 20+ methods, such as the List interface. And you want to create a new implementation of this interface, which is almost identical to an existing implementation, except for one tiny difference. Example, you want an CustomArrayList implementation that doesn't allow the number 666 to be populated into the list.

With inheritance, you can accomplish this in just a few lines of code. Extend the existing implementation, and override just the methods that need to be overridden.

Whereas with composition, you now need to manually implement all 20+ methods in the interface, just to make the pass-through call. This adds a tremendous amount of boilerplate to the code.

Depending on how many methods are in the interface and how invasive the changes are, this boilerplate is sometimes worth it and sometimes not worth it. Ideally, languages will add built-in support to facilitate this pattern without the associated verbosity. But until then, people will continue to use inheritance just because of how much less verbose it is.

>Whereas with composition, you now need to manually implement all 20+ methods in the interface, just to make the pass-through call. This adds a tremendous amount of boilerplate to the code.

Inheritance is not necessary for this. The traditional way of achieving this in functional languages is to use a closure to return an object/record. Instead of brittle inheritance, just pass this object to another function that returns an object modified however you want it. Objects can be combined too, achieving the same goal as multiple inheritance, but less dangerous. Simple, easy, succinct, composable.

I agree that inheritance is not necessary for this, if languages provided better built-in support for the composition pattern. I was referring to the downsides of using composition in today's "enterprise" languages like Java.

Ideally, languages will add built-in support to facilitate this pattern without the associated verbosity. But until then, people will continue to use inheritance just because of how much less verbose it is.

Well, you can somehow achieve a part of it in Python with implementing magic __getattribute__ method:

  class CustomArrayList (object):
    def __init__(self):
        self.list = ArrayList()
    def add(self, item):
        if item == 666:
           raise
        self.list.add(item)

    def __getattribute__(self, key):
      """For rest of the methods use them as they are.
      """
        try:
            attr = object.__getattribute__(self, key)
        except AttributeError:
            attr = object.__getattribute__(self.list, key)
        return attr

However, most probably no one will like you if you use this method :)

Duplication is better than the wrong abstraction

Inheritance is not necessarily the wrong abstraction, too.

Maybe, but who says inheritance is the wrong abstraction?

Can you clarify this idea some?

I have used inheritance in a way to make accessing code more seamless and easier for development. But without inheritance, I end up with a lot of boilerplate code, imports, etc...

Doesn't duplication go against the DRY principle? I know you are saying "wrong inheritance", but some people are saying all inheritance is wrong...

The semi-anti-inheritance stance would say that inheritance from an abstract class is acceptable.

I believe this would work for you.

My little rule of thumb is to inherit if the new implementation is a 'pure' over the inherited class. That is, I'm not introducing any _new_ changes to the state of the class.

automatic code generation would be a way to do it without inheritance and not manually needing to implemenet all 20+ methods.

Code generation tends to result in bloated binaries and excessive runtime memory consumption (unless your compiler is especially clever about optimizing out the redundancies).

Yes, but you still need to create a code generator first. If your language of choice allows to do it nicely.

Automatic code generation is an incredibly effective problem factory.

Exactly. I learned pretty early that inheritance relations can be trivially refactored into a delegation based design and that there's a difference between type inheritance (aka. interfaces) and implementation inheritance.

IMHO inheritance and especially deep inheritance hierarchies are almost always the wrong thing to do. I know of few exceptions and have ended up regretting breaking that rule on the few occasions I allowed that to happen. These days I just don't use it at all on principle. I'm very weary of using frameworks that depend on or over use inheritance. E.g. much of Spring looks problematic and convoluted to me. I use it but I tend to avoid the stuff that is too hard to understand. Five or more layers of classes is just insanely misguided IMHO.

Most of those layers are just working around the previous (wrong) decision to use inheritance. It's like the broken windows theory. Inheritance leads to more inheritance. It causes all sorts of problems down the line and you can't change it once you have users extending your classes.

I love that modern languages disable this. E.g. Kotlin has closed classes by default (the opposite of Java) and does not allow inheritance between data classes at all. This is great and communicates clearly that you should not be littering your code base with 'open'. This encourages good design that does not depend on scattering functionality all over the inheritance hierarchy or the endless levels of indirection. They even provide a compiler plugin to deal with spring that re-opens classes at compile team so that Spring and other legacy Java framworks can do it's dirty business of reflectively extending classes without requiring the code to be compromised.

I find it ironic that e.g. the Javascript community has worked hard to get classes and inheritance and are essentially repeating all the same mistakes people were making with Java 20 years ago by overusing inheritance. Most of 'modern' javascript to me looks like a blast from the past.

> I find it ironic that e.g. the Javascript community has worked hard to get classes and inheritance and are essentially repeating all the same mistakes people were making with Java 20 years ago by overusing inheritance. Most of 'modern' javascript to me looks like a blast from the past.

IME JS classes are less about inheritance (which remains compositional anyway, though classes do make these easier what with not having to maintain the prototype chain or hand-roll super calls) and more about the various syntactical convenience of class declarations, namely that you don't have to deal with the Function / Function.prototype crap, the hand-rolling of `new` mandates (a class ctor is always called through new), the requirement of explicit strict mode (class declarations are always strict), method shorthands (they do exist on object literals, they don't exist when adding to a prototype property by property), …

I just don’t get the class/prototype approach, honestly. It really seems to me that you get almost all of the benefits and more by just returning an object from a closure, which has the extra benefits of encapsulation and using only simple language features that a JS user pretty much has to use at some point:

    const createCounter = ({ startAt = 0, incremementBy = 1 }) => {
      let count = startAt
      return {
        currentCount: () => count,
        step: () => {
          count += incremementBy
        }
      }
    }

    const counter = createCounter({ startAt: 5 })
    counter.step()

versus

    class Counter {
      constructor({ startAt = 0, incrementBy = 1 }) {
        this.startAt = startAt
        this.incrementBy = incrementBy
        this.count = 0
      }

      step() {
        this.count += this.incrementBy
      }
    }

    const counter = new Counter({ startAt: 5 })

JavaScript classes are pure syntactic sugar for object constructor functions. If the syntactic sugar does not make your code cleaner then don’t use it.

Methods with arrow syntax offer implicit function binding and TypeScript adds abstract classes as well as abstract, private, protected and readonly fields. New language features aren’t supposed to replace simple logic that has always worked. They are there to provide new options for programming patterns.

In my experience, It's pretty rare to see inheritance used in anger in modern JavaScript. Frameworks may have you extend base classes as their primary API, but they don't tend to encourage that you implement your own deep inheritance tree.

I think the last time I personally abused inheritance was when using Backbone.js more than 5 years ago, and that experience was what finally tipped me over the edge to start learning more about functional programming.

> I learned pretty early that inheritance relations can be trivially refactored into a delegation based design

You can go much farther and discover that OO state mutations across multiple methods can be replaced with higher order functions that let you keep state mutations local, within context of each function. Suddenly OO becomes this weird very unproductive and error prone way of writing and reading code. An entire OO concept is just bad, always was, nothing can fix it.

At least with Javascript higher order programming was always possible.

What are you referring to? Could you give an small example (in JS or any other language)/links/for me to chew on?

That is one subjective question, OO is not that well defined beyond being oriented around objects. Heck, the Treaty of Orlando from 1988 says a lot more about the open definition of OO.

Sandi Metz does a far better job explaining the proper use of OOP in this video: [0]

I highly encourage anyone with doubts about OOP to actually complete that Kata.

In short, inheritance should be confined to removing conditionals in problems with shallow-wide [1] inheritance graphs, where things truly "is-a" thing, not "have-a" thing [2]

Real life examples I've encountered: * buttons in a toolbar implementing a command interface * database drivers extending a base implementation * web-server endpoints extending a base implementation

Some of the most complex software in the world is currently modeled using OOP. If one is ever in doubt, look into creating plugins for IntelliJ. The whole program is a massive exercise in OOP modelling, and it works pretty well (if not a little slow some times) [3]

[0] https://www.youtube.com/watch?v=8bZh5LMaSmE [1] http://cek.io/blog/2014/05/26/poodr-ch-7/ [2] https://stackoverflow.com/questions/2218937/has-a-is-a-termi... [3] https://www.jetbrains.org/intellij/sdk/docs/basics/getting_s...

those 3 annoy me...

I'd go with 2:-

- messages

- objects that have conversations with other objects through messages to achieve a cohesive purpose

inheritence is essentially a method of sharing code without going through a message, so not really OO, you can use any sharing mechanisim you like to make cohesive objects.

that's too vague. Most OO PLs don't actually use messages in any way under the hood (except maaaybe ruby? I hear things but haven't peeked at the MRI code) and use messages as a "conceptual framework" but let's be honest - is calling a method owned by object A.do_something(B::target_type, C::parameter_type)... What sort of a message is that?

moreover, plenty of FPs (I'm looking at you erlang) use message passing all over the place, as, arguably the most important feature of the language, with things that vaguely look like objects (gen_servers) but I would not really call erlang an OO language, except maybe to joke to an OO programmer that an FP is truer to the original intent.

Inheritance / encapsulation / polymorphisim are kind of vague too.

actually, Alan Kay said Erlang was most like his concept of OO.

Ruby has some nice hooks for when an object doesn't have a method, at which point you can dynamically resolve it. Much advice in the OO world and its principles are really just to do with message routing, and a lot of Design Patterns are about how to do it when the type system fights you

but even if you are stuck with your C++/Java/C# type languages, then I think it is still useful. I've often seen in the first 10-15 minutes with "traditional" advice that set off down a path of design that ultimately causes a lot of struggle between OO and the typing system, most often because of naming things too early warping the mental rather than recognizing traits of interactions.

IIUC Kay had a live organisms in mind, passing biochemical signals at will, which Erlang matches quite snug.

It's so odd because when people talked about OO I imagined something live and parallel, kinda like Kay/Erlang buuut it was so far from that.

The first OO language, Simula 67, was exactly like that.

True, I almost forgot. Wasn't the model a bit slow (relatively speaking) at the time ? Maybe that's why it disappeared for a while.

Simula 67 was designed for simulations (hence the name), it wasn’t general.

Actually, the first OO language was probably SketchPad, but it’s object model isn’t very recognizable compared to textual OO language.

I think Ruby qualifies as true OO (in the Alan Kay sense) because messages are first class entities that can be explicitly manipulated. This makes it trivial to implement lots of OO patterns that require a significant amount of boilerplate in other languages. For example, a proxy.

Erlang makes messages an even more central element, as the whole language is built around the concept of inboxes and asynchronous message passing (synchronous message passing being a special case).

Better type systems are in vogue now, for really good reasons. But I wish we don't ignore lots of good ideas from dynamic languages like Erlang or Mozart/Oz. Every time I open CTM or SICP I find great insights I had already forgotten.

could you explain "messages are first class" a bit more? what does that look like in Ruby?

Avdi Grimm has an explanation [0] more worthy than what I was managing to conjure up.

[0]: https://www.rubytapas.com/2012/10/17/episode-011-method-and-...

Interfaces or bases classes where all methods are pure or empty are often used to implement messages in awkward ways in mainstream OOP languages as the languages lack proper union types.

I assume you pass pointers around to share data? How do you handle cleanup?

It was a trick question: two are optional.

(I pity the educator if he or she didn't know this.)

If you eliminate polymorphism and inheritance, is what's left really all that useful?

The one we can dispense with is encapsulation.

Polymorphism, no; I mean, how can we substitute different kinds of objects into the same situations dynamically without polymorphism. OOP is almost synonymous with polymorphism.

But we do not have to bundle code and data representation together; there are other approaches to OOP, like generic functions.

I don't think we can dispense with encapsulation and still have OO, though. Sure you can program without it. You can even make good programs without it. You may even be able to make better programs without it :-) However, it won't be OO.

The idea behind OO is to move away from data-centric programming. If I have a system dealing with geometry, I can have a Point object that has an x and y coordinate. However, once I have a Point, I should be trying to make my system so that I no longer access x and y directly. X and y are "encapsulated" in the Point. Collaborators should use the functionality on Point to do what they need to do, rather than trying to pry Point apart and get at the data.

Of course, barely anybody writes "OO" code like that, even if they espouse to follow "encapsulation".

I would argue as well that generic functions do not, in themselves offer an OOP environment. You need one more thing: partially applied functions. If you can create a partially applied function, you can bake in some program state and pass it around, offering functionality on that program state. However, nobody on the outside can access that state. This is the encapsulation necessary for OO.

Point = {x, y} is a strange example. What exactly is being encapsulated? Any Point structure I've ever seen has accessors for x and y, and no other internal data.

In general, I don't see the need for encapsulation in order to qualify for object status. The classic counterexample is CLOS, which doesn't have it -- and the debate over that has been raging for decades [1].

[1]: http://wiki.c2.com/?HowObjectOrientedIsClos

The best basis for the essence of object-orientedness that I ever read was suggested in an article that focused on identity. (I don't remember where I saw this -- possibly from Kent Pitman?) If you could guarantee that some value is exactly the same as a value that you had earlier, and not just a mostly-copy but identical in every respect, then you had an object. Everything else falls out of that.

This is a great question. I thought that myself, so I tried to make a system where I couldn't access x and y. It turns out it's completely reasonable to do so. If you want to move a point, you add a translate method. If you want to compare points you can. You can add and subtract points. If you want to align a group of points on the X access, you can write a method on point to do it. There were very few times when I wanted to actually access x and y rather than act on it.

I do agree, though, nobody actually writes code like that. Does that mean that I think nobody actually does OO? I hadn't actually thought it through that far :-) I think this is why the concept is so vague (your excellent example being a great indicator of that). C++ is often referred to as "C with Objects" and I sometimes think we've gone so far as to say anything with a function that operates on a structure is "Object Oriented". If so, I think we've lost our path a little bit.

You can keep adding mathematical transformations to the Point object all day long (though at some point you'll realize the mathematical operations don't belong there, and the concept of "point" isn't abstract enough - the study of right abstractions here is called "algebra"). But there comes a moment when you want to draw that point on the screen, and suddenly there's a good chance you'll have to access individual components, because the API of your drawing device doesn't understand your particular Point class.

Arguably this is still within purview of "Point" abstraction, but:

> If you want to align a group of points on the X access, you can write a method on point to do it.

This calls for a static method really, otherwise the abstraction becomes subtly wrong. And with static methods you quickly realize that you're using the containing class as just a namespace.

CLOS actually resolves this nicely by having methods being their own things separate from classes. As a related side effect, the typical C++/Java case of "object methods" isn't a special thing in CLOS, it's just a method that happens to be polymorphic only on its first argument. The abstraction around methods seems cleaner, and the class in CLOS is just responsible for encapsulation and inheritance, not for namespacing methods.

It sounds like all you're really doing is taking any function that does want access to X and Y, and shoving it into the Point object where it has that access. Or to put it another way, you're defining any function that wants access as "part of the concept of point". You can indeed accommodate any code with this transform, but is it the right thing to do? Do you gain anything by bloating up 'point' with transformations and comparisons and alignment operators and so on?

Of course you gain something. By encapsulating all methods that operate on X and Y in a single place, Point (where X and Y are defined), it is now _much_ easier to change X and Y. It's all right there in one file.

Point {x, y} may not be the best example, but you can certainly see how this can be beneficial should X or Y become something even slightly more complex. And this is the purpose of encapsulation - to make a system easier to understand and therefore easier to change.

The Point could internally be represented in a polar coordinate system.

I kind of agree that encapsulation isn't needed for object status. The caveat only being that it would be a weird object system where you could be sure there was no encapsulation.

I mean, OK, in some languages you know that. But does it change anything important?

https://en.wikipedia.org/wiki/Polar_coordinate_system

Even if a point uses polar coordinates internally, we can have syntax "p.x" which gets the Cartesian x.

Information hiding is an important concept in low-level-ish systems programming languages in which p.x implies a piece of machine code that offsets 24 bytes from the base address of p, and fetches a four byte integer.

This Point class is a poor example because it does not have anything that is not part of its interface, and, as presented here, does not have any constraints on it.

The intended purpose of encapsulation is to try and preserve integrity of a system by restricting the ways a programmer might put it into an inconsistent state. Knowing that certain constraints are in place simplifies the problem of understanding and debugging a system.

Python is build entirely around the idea that encapsulation is mostly useless. "We're all consenting adults" is the general philosophy. As long as there's a convention as to what properties are "public" and which are not, a motivated user of a class should be able to do what they want with it.

There's no point in putting a "private/public/protected" security model in a programming language. It isn't a security boundary.

This vastly simplified the design of OO in Python, and it makes testing far far easier. There's no need to go through the dependency injection acrobatics in order to change one method for testing or proxying.

(There technically is a way to munge a property name in Python but its use is discouraged).

I wish there was a "do not touch unless you know what you're doing" field. Private fields and members are a nuisance if you need to do some unsupported thing with a library. On the other hand, there are often utility functions in an object that are absolutely only ever meant to be used by that object itself, and not to be called from the outside.

Python supports those by prefacing with "__", IIRC.

There's no point in putting a "private/public/protected" security model in a programming language. It isn't a security boundary.

It’s about intention. If I mark a property or method as private, it means that I can get rid of it, rename it or change the expected behavior without considering it a breaking chance.

Yeah, and Python has some standard nomenclature for marking a property as protected and a little bit of behavior for helping mark it as private. You do not need encapsulation for that.

And there is nothing about the Pythom runtime stopping someone from using it anyway.

With a statically typed language, you really have to go out of your way to do it like using reflection and if your code breaks on an update you get what you deserve.

YAGNI rules the day.

You’ve never had to refactor code that was used as a library by other developers?

Do you realize how many hacks is built into Windows just because developers were using undocumented features?

> (There technically is a way to munge a property name in Python but its use is discouraged).

Do you have a reference for that (i.e. the discouraged part)?

Note that "encapsulation" refers to two completely different things, one of them by mistaken application of the word:

- combination of methods and data

- information hiding

Information hiding is needed for OOP, but it can be hidden in the implementation. The fact that if I have a point object, I can access point.x is not an example of information hiding being violated. Firstly, it doesn't interfere with polymorphism: the same point.x code can access the x coordinate of points of different types. Secondly, the syntax point.x can actually be a method call which invokes an accessor under the hood, so the object doesn't actually have to have a slot x. There is no semantics or "moral" difference between having a pair of methods point.getx() and point.setx(<number>), and just a point.x. Lastly, sometimes it is perfectly acceptable in an object design to have trivial properties.

Information hiding is more important in languages like C++ because an access like "point.x" compiles to code which assumes that x is at a particular offset in that object, and is of a particular type and so forth. It's less important in a dynamic language in which we can cafely ask for the x slot of any object.

Encapsulation of methods and data isn't required in an OOP system; OOP systems like CLOS work without it just fine.

I'm pretty sure Perl's Native OO has no encapsulation, at least without custom modules or weird wranglings like inside-out objects. It doesn't mean we must peek inside, but the option is there. It is completely functional, but as prone to misuse as the rest of Perl.

One should note that in Perl 6, object encapsulation is complete. You can only directly access attributes inside a class, and only through (usually autogenerated) methods outside of it.

"The one we can dispense with is encapsulation."

To me this is the most important part. I like to have private or public, protected is not needed.

I agree that code representation should be kept separate.

> To me this is the most important part. I like to have private or public, protected is not needed.

OO's encapsulation is about bundling data and operation, not about information hiding, and as kazinator noted generic functions (as in CLOS) prove you can have OO just fine without.

As to information hiding, there are many fine OO languages which don't have it either (Python probably being the prime example there, but I'd say it also applies to languages like Ruby where you can trivially override existing ACL) so it's clearly not necessary either, let alone "the most important part". Especially as conversely many non-OO languages do have access control, hinting that the two are quite likely orthogonal.

Information hiding is useful for engineering and resilience, not for object orientation.

As to private / protected / public, I'd argue it's private which is the least useful (since we've already ascertained none is actually needed): it's literally just hiding stuff from yourself. I think removing that level of ACLs is one of the few good idea Go had.

ACLs also seem to mix concerns. The "private" concept is essentially making life difficult for yourself, but having a built-in mechanism for separating public interface from internal code, that's a bit more than just convention, is useful. For instance, in Common Lisp there's no language-enforced ACL, but when building modules (that may or may not involve a class, or many classes), I assign a package for each module and make it export only the symbols that represent its public interface. In code using that module, this becomes a syntactic difference in a way you refer to these symbols - module:foo means "foo exported from package 'module'", while module::foo means "foo internal to package module". That simple isolation, completely overridable with an extra colon character, is enough to clearly communicate what is and what isn't a part of an abstraction.

Is there a warning when someone overrides that isolation? In C# you can also access private members through reflection and I have seen people use that a lot instead of bothering to understand why the original developer decided to make the variable private.

No, there isn't, because "we're all adults here". But you have to type :: instead of : to do this, which usually tells you something, and you don't have to go through reflection to do this, so such overrides don't cause performance issues. Common Lisp doesn't prevent you from accessing anything.

I wish we he had more adults instead of people fresh from college who think that best practices and things to avoid are obsolete and don’t apply to them :)

That's the unfortunate nature of exponential growth. If the number of programmers doubles, say, every 3 years, that means at any point in time, half of the workforce has less than 3 years of experience.

I mean, you can do pure functions. And those pure functions can operate on structs. And, once you're there, it's probably good hygiene to keep all the functions operating on a given struct in one file.

Congrats, you're back to 'encapsulation'! Encapsulation is actually the only important tool in that particular toolkit. We're mortals, we need coping tools to keep programs manageable.

That kind of "encapsulation" is simply storing code together with the data it belongs to (good practice) and possibly namespacing it together. It's not what they mean by "encapsulation" in OO courses, though it's arguably the only benefits "encapsulation" give you.

Would you be interested in doing a podcast together about programming? I'm a radical javascript programmer (search ONNEMI-4211). You seem smart. I've never made a podcast before.

On the one hand, you've got some amazing satire here, on the other hand, I'm a little insulted that it's directed at me of all people.

Upvoted anyways :)

Satire?

I like to use classes almost exclusively as a way to couple an object with methods directly related to it. Basically structs with methods. Useful enough for me.

I was taught that there were 4 tenents, inheritance, encapsulation, polymorphism and abstraction.

I've noticed OO education has a habit of appropriating every good idea from software engineering as if it was a distinctive feature of OO approach. I think reading SICP opened my eyes to that for the first time. As it turns out, you can do abstraction without objects just fine.

What OO education? I find that people just fling around random tenants when they talk about OO, even worse when they talk about FP. Even crazier is when some darling FP technique like entity component systems specifically use a synonym for object (entity) to avoid being called OO.

> I was taught that there were 4 tenents

> I find that people just fling around random tenants

It's tenets. TENETS.

Please do not fling around random tenants! We'll have to re-plaster the walls again!

Sorry, my post is too old to edit. I did get a nice chuckle out of this, though.

Entity Component Systems is an FP technique now? That's new to me.

ECS is one of the bigger confusion of ideas out there. The articles about it tend to mix together at least three of the following, each in different proportions, and without realizing it: composition over inheritance, relational data model and SoA/data-local design.

IMHO, the relational data model is the more fundamental part of ECS. Struct-of-arrays is a bit lower-level of a view on the same (with more emphasis on performance and less on architecture), and composition-over-inheritance shows up elsewhere (although the mechanism for composition is _not_ at the language level, where most people expect it to be).

Once you have the relational model, the Systems part of an ECS architecture almost defines itself as you figure out how to work with your data.

But entities really are not objects, because they neither send nor receive messages, and because they have no associated data (and therefore no encapsulation). In fact, the component-system relationship encourages you to break encapsulation.

OO is just programming with objects, regardless of how you coordinate them. Encapsulation is a multi dimensional thing, ECS just favors one form of encapsulation over another.

I'm not a fan of that as a definition: To me, object-orientation means modelling computation as communication between stateful objects. An object-oriented programming language has features that facilitate such a design. Inheritance would be such a feature, but it could easily be substituted with other ways of subtyping and code reuse.

Absolutely. Tight coupling between data set instance and function that manipulates this data seems to be the current definition of object-orientation (as opposed to something more philosophical like "living entities communicating together", which is a bit vague IMHO).

Rather than having one big memory chunk, and one big function chunk (like the old DATA DIVISION and PROCEDURE DIVISION of cobol), you divide thoses into smaller data+procedure bits that idealy map to existing concepts from your domain.

That seems like a much more effective way of seeing the thing. Although once you start adding parallelism and asynchronous communication, you do probably end-up in something closer to the Kay definition.

Isn't abstraction a tenet of every programming paradigm?

Seems like in some languages, inheritance is not optional if you want to use polymorphism.

AFAIK in C++ you must use inheritance if you want polymorphism since there is no real concept of interfaces.

You can use templates to perform static polymorphism and duck-type the calls.

If you want to do things the Java or C# way, then you're correct. You'd want a pure virtual interface, which mimics what you'd get with Java or C#.

With all this angst against OOP, what other alternatives should a programmer consider or what patterns of hierarchical logic do people suggest?

Hierarchy - a single ontology - is one of the problems with OO. Ontologies - note the plural - are useful, but choosing just one ontology privileges some axis of abstraction over others, but there are different lenses you can put on things that may make you want to classify by different criteria.

For example, you might have a bunch of things, some of which: (a) can be rendered in some display - could be console, HTML, print output, screen, don't care; (b) can be serialized to a variety of media; (c) have some common configuration, that interacts with some configuration management system; etc.

If you try and shoe-horn these commonalities into a hierarchy, you end up with classes that advertise being able to do too much and need to have "not implemented" error conditions, breaking the Liskov substitution principle.

Interfaces are a way of breaking out. They're additive, rather than hierarchical, from the implementing class perspective.

The other big problem (a bigger problem IMO) with inheritance is coupling. I don't think there's any closer coupling between two pieces of code in an OOP system than inheritance. Changes in a base class can radically alter behaviour in all descendants. Depending on the implementation of overriding, descendant behaviour can be accidentally hijacked with no compile time or run time warning merely by updating a dependency. The API by which base class and descendant class interact is bidirectional, with the flavours of both library (you call them) and framework (we'll call you), and intermediate internal state when e.g. overridden protected methods are being called is usually sorely undocumented and liable to change.

> Interfaces are a way of breaking out. They're additive, rather than hierarchical, from the implementing class perspective.

Java (and .Net by copying) choose to make interfaces additive and superclasses combinatorial. It's a design decision and in no way intrinsic. Other languages have different choices.

Oh, I'm aware. However additive superclasses are much much worse for OOP, there's good reason languages beyond C++ haven't walked the same road.

Use composition for reuse and interfaces for polymorphism. These can do the same as inheritance and more, and they do it more cleanly. Reuse and polymorphism are orthogonal concerns that inheritance tries to fuse awkwardly together.

Try Go if you’d like a familiar language without the inheritance that you can pick up in an afternoon.

It's not compulsory even in a language that supports it, I'm working on a medium sized C# project that has minimal use of inheritance and only then to fit in with the requirements of a library feature.

Yeah, I meant it as a learning suggestion, not a “switch your main language” suggestion. Fully agree with you.

The first question should be whether we need hierarchical logic, or what hierarchical logic is supposed to be.

It's even harder to define (which might be why OOP is so popular --- it's easy to get dogmatic about "OOP is X", and the cargo-culters will pick it up and spread it like religion), but I'd say "be pragmatic and let it come naturally". Systems tend to naturally form OO-ish things even if they're not written in an OO language; the Linux kernel is one example. I think of OO as just another layer of organisation beyond functions and structures, arising from the desire to group related data and code together.

It's not natural. It depends on your previous experience. Preferring C-style semi-OO stateful programming and OO merely shows what influenced your thinking.

In my opinion we need look at bringing the relational model into code, not just data. OOP is too awkward for complex relationships. Or, at least making code more relational-friendly to avoid the O-R-Impedance-Mismatch: https://en.wikipedia.org/wiki/Object-relational_impedance_mi...

There's nothing particularly wrong with OO as a programming paradigm when used for the right purposes. It was originally designed for simulating real world systems and still works great for that.

Aren't most large systems organized in an OOP manner?

> and then asked us which one was optional

Python manages quite well without encapsulation.

Identity is the most important characteristic of OO. Objects have identity.

This very article ends with '"¿Por qué no los dos?", which means "Why not both?"'. I agree, use both, but don't get carried away with either. If you exclusively use composition you're basically reinventing inheritance anyway, with more steps.

But the linked article is reasonable. Less reasonable articles like this one exist, however: https://codeburst.io/inheritance-is-evil-stop-using-it-6c4f1...

These are the articles where someone saw that the "cool kids" don't like/use inheritance, and so adopted the position to try and be "cool".

Don't try to be cool, try to understand. Inheritance doesn't say, "Create a complex inheritance tree of interdependent classes". That's the strawman. Remember that.

> when my software engineering professor listed the 3 fundamental tenets of OO—inheritance, encapsulation, and polymorphism—and then asked us which one was optional.

None of these is a fundamental tenet. See the article linked here [1]. The fundamental tenets are the five "SOLID" [2] principles.

Object-oriented design is not well-taught in general. The impression most people normally have of it is quite different from what it actually is.

P.S. You may also find [3] interesting.

[1] https://news.ycombinator.com/item?id=18250255

[2] https://en.wikipedia.org/wiki/SOLID

[3] https://news.ycombinator.com/item?id=16468796

I'm not a huge fan of SOLID. It's treated as a pillar of software development, but I feel like some of the advice sounds good or is right but isn't terribly useful(SL), one was so terrible it was rebranded(O), and some are a useful tool more than a design goal(ID).

Single responsibility principle - something we can all agree on but doesn't help you decide between two non hideous designs

Open/Closed Principle - the original advice was so terrible that we ignore it and pretend it means something else that has very little to do with open/closed

Liskov - technically true but very few applications are bad or incorrect because of this violation(especially with the recent move away from inheritance)

Interface Segregation - Sure it's useful to split up interfaces sometimes.

Dependency Injection - Sometimes useful for testing or IOC.

This seems very much like a semantic debate. Either OOP is characterized by inheritance—which is consistent with the notoriously “OOP” languages like Java, C#, and C++<11 and probably the overwhelming majority of intro-to-OOP literature—or you exclude inheritance as a hallmark and make it so general as to be indistinguishable from many other paradigms, many of whom came before it. If the latter, why bother fighting the semantic debate at all? If OOP really is that unremarkable, why advocate for it as a meaningful label instead of advocating for SOLID generally?

Can't the SOLID principles apply equally well to functional programming by just replacing "class" with function, object, or type (depending on the principle)?

Single Responsibility is achieved by composition

Open/Closed is probably the one that fits least with FP, but it seems like FP achieves the same result by replacing both extension and modification with composition.

Liskov Substitution can be replaced by a subtyping or duck typing.

Interface Segregation seems like its more about design than programming. However, to the degree that it applies to programming, composition seems like it actually better meets this principle than inheritance.

In terms of Dependency Inversion: If anything, it seems like one of the biggest problems with FP is that it makes it easy to take this principle too far by making things too abstract (e.g. the category theory aspects of languages like Haskel seem like they could easily be abused).

I'm not super experienced with OO so am I maybe misinterpreting these principles?

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