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Comment by Rochus

5 days ago

> The industry and the academy have used the term “object-oriented” to mean so many different things.

I think we can safely stick to how IEEE defines OOP: the combination of three main features: 1) encapsulation of data and code 2) inheritance and late binding 3) dynamic object generation (from https://news.ycombinator.com/item?id=36879311). Message passing (the feature the article claims is unique to Smalltalk) is mathematically isomorphic to virtual method dispatch; and also Smalltalk uses method dispatch tables, very similar to C++ and Java.

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Rochus

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jillesvangurp  4 days ago

The problem with that definition is that modern languages like Rust, Go, and Javascript fall between the cracks here with de-emphasizing things like classes and inheritance while still providing things like generics, interfaces, encapsulation, etc.

For example, Javascript was influenced by a few languages, one of which was a language called Self which is a Smalltalk like language where instead of instantiating classes you clone existing objects. It's a prototype based language. So, there weren't any classes for a long time in Javascript. Which is why there are these weird class like module conventions where you create an object with functions inside that you expose. Later versions of ECMA script add classes as syntactic sugar for that. And Typescript does the same. But it's all prototypes underneath.

Go has this notion of structs that implement interfaces implicitly via duck typing. So you don't have to explicitly implement the interface but you can treat an object as if it implemented the interface simply if it full fills the contract provided by that interface. Are they objects? Maybe, maybe not. No object identity. Unless you consider a pointer/memory reference as an identifier.

Rust has traits and other constructs. So it definitely has a notion of encapsulation, polymorphism, etc., which are things associated with OOP. But things like classes are not part of Rust and inheritance is not a thing. It also does not have object identity because it emphasizes things like immutability and ownership.

Many modern languages have some notion of objects though. Many of the languages that have classes tend to discourage inheritance. E.g. Kotlin's classes are closed by default (you can't extend them). The narrow IEEE definition is at this point a bit dated and reflects the early thinking in the sixties and seventies on OOP. A lot has happened since then.

I don't think a lot of these discussions are that productive because they conflate a lot of concepts and dumb things down too much. A lot of it boils down to "I heard that inheritance is bad because 'inject reasons' and therefore language X sucks". That's maybe a bit harsh on some languages that are very widely used at this point.

  • throwup238  4 days ago

    > Rust has traits and other constructs. So it definitely has a notion of encapsulation, polymorphism, etc., which are things associated with OOP.

    Why do you associate polymorphism with OOP? It’s a pretty universal PL concept. Haskell’s polymorphism is one of the defining features of its type system.

  • Rochus  4 days ago

    Well, C++ also has higher-order functions and lambda expressions, and yet we don't call it a functional programming language.

LukeShu  5 days ago

Inheritance is just the unnecessary coupling of composition and polymorphism.

  • saghm  4 days ago

    Even before I got to the point where I decided I didn't like inheritance, I distinctly recall having conversations about how I felt that using inheritance for anything other than polymorphism didn't usually end up with particularly clean code. I can remember a conversation about this at least as far back as the summer after my freshman year of college, and I don't think I was aware of the idea of "composition" yet, because I remember phrasing my point as something like "inheritance shouldn't be used for 'code-sharing', only for polymorphism".

    • lukan  4 days ago

      Out of curiosity, when you say you don't like inheritance, does that mean you never use it at all, or you only use it rarely?

      Because even though inheritance often is used in a wrong way, there are definitely cases, where it is the clearest pattern in my opinion.

      Like graphic libary things. E.g. everything on the screen is a DisplayObject. Simple Textfields and Images inherit directly from DisplayObject. Layoutcontainers inherit from DisplayObjectContainer which inherits from DisplayObject.

      Inheritance here makes a lot of sense to me and I don't see how it could be expressed in a different way without loosing that clarity.

      7 replies →

  • o_nate  4 days ago

    Inheritance is not necessary, but then very few programming constructs are absolutely necessary. The question is does it help program clarity or not. I think that in some cases, used sparingly, it can. The main danger of inheritance is not that it is OO, but that it is not OO enough. It breaks encapsulation by mixing properties and methods between base classes and derived classes without clear boundaries. Composition is safer because it preserves encapsulation. In general, I think that protected abstract methods are a code smell, because they usually indicate close coupling of details that should be kept separate between the base and derived classes. But used correctly, inheritance can be more succinct and convenient.

  • pjc50  4 days ago

    Delegation is a very useful part of composition. Almost all OOP languages have two techniques to delegate some methods to another object:

    - manually write a bunch of forwarding methods and remember to keep them updated, or

    - inheritance.

    • bccdee  4 days ago

      To be fair, the compiler generally forces you to keep the forwarding methods updated. It can be irritating, but there's little risk of forgetting in a statically-typed language.

      Manual forwarding also operates as a forcing function to write small interfaces and to keep different pieces of logic separated in different layers, both of which feel like good design to me. (Though I'm not saying I'd turn my nose up at a terser notation for method forwarding, haha.)

    • LukeShu  3 days ago

      ...yes? Hence me saying that 'composition' and 'polymorphism' have often been unnecessarily coupled together in 'inheritance'?

      Compare: Ruby mixins or Go embedded struct fields.

vips7L  4 days ago

Object orientism is just encapsulation. It’s the only thing that is required. You can have objects without inheritance and virtual dispatch.

  • bccdee  4 days ago

    Languages like Go and Rust have module-scoped visibility, though. This is definitely encapsulation, but I wouldn't call it inherently OO.

  • vbezhenar  4 days ago

    So Python is not OOP language? You can't hide fields.

    • nr378  4 days ago

      You can hide fields in Python with a little bit of gymnastics:

        class EncapsulatedCounter:
      def __init__(self, initial_value):
          _count = initial_value

          def increment():
              nonlocal _count
              _count += 1
              return _count

          self.increment = increment


  counter = EncapsulatedCounter(100)
  new_value = counter.increment()
  print(f"New value is: {new_value}")

      1 reply →

cjfd  4 days ago

(1) and (2) sound reasonable enough. What do they mean by "dynamic object generation"?

  • cess11  4 days ago

    Runtime instantiation.

    From the link above:

    "Instead of seeing a program as a monolithic structure, the code of a SIMULA program was organized in a number of classes and blocks. Classes could be dynamically instantiated at run-time, and such an instance was called an "object". An object was an autonomous entity, with its own data and computational capabilities organized in procedures (methods), and objects could cooperate by asking another object to perform a procedure (i.e., by a remote call to a procedure of another object)."