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0 pointsdidibus7y ago0 comments

> This seems completely circular to me. Your definition of OOP is really "whatever all OOP languages do"?

It seems logical to me that for two things to be grouped together in the same category, some commonality between the things are required. So there has to be something in common with all OOP languages which makes them OOP. Otherwise, it is not possible for them all to be OOP languages.

You're saying a language supports OOP if it has a protocol like construct. Sure, you can decide to define OOP as such. But then languages commonly refered to as supporting OOP, like Java, get excluded. So it seems to me it's a bad way to define OOP if it excludes Java, which is probably the most cited language when talking about OOP.

> What is OO to you?

It's a paradigm. Where your program models the problem using a concept known as an object. Characterised by the grouping of data fields and procedures responsible for accessing and modifying said fields. Objects know about both their fields and their methods. Where other code can only access the object's fields and the object's methods through a reference to the object itself. A pure OO language would have everything modeled this way exclusively. Thus nothing would exist outside an object, and you'd only have objects interacting with other objects. An impure OO language, thus a multi-paradigm language with support for OO, would allow part of your code and data to be modeled this way through objects, and other parts using other paradigms.

Without resorting to interop, Clojure/Script, to my knowledge, does not have an object construct which fits this definition.

> from a perspective of message passing. A message is passed to the record and based on its pedigree it decides how to respond

The call isn't made to the record, but to the protocol function. A function is called, and this function decides what to do based on the type of the first argument.

> Plenty of OO languages don't have private data and allow direct access to object fields. Arguably, by your definition, it isn't OO at all to even provide for public fields

Those are impure OO languages, they are multi-paradigm. If you were to make all your data inside objects public, and never put any methods on the objects. And you would put all your methods outside of objects, or inside objects with no data and have them take objects with data as their first argument, then your program is no longer using the OO paradigm, it is no longer object oriented.

> As long as the methods follow the data around or vice versa, in my view, encapsulation has been achieved

Clojure/Script records don't have their methods following them around. You can define the functions for the protocol in another namespace, and then you have to require them separately. They don't tag along with the record.

> A record implementing a protocol can receive method calls. All of its method implementations happen with the records own fields in scope (assuming you define them in the defrecord)

Again, the call is made to the protocol functions. Simply importing the record does not make these functions exist within your namespace, you need to require them. And these functions are not scoped within the record. They don't see the fields, they need to access them through the record, like any other function would. Nothing is special about these functions. They're just functions that know how to do something to a concrete datatype.

> As I understand it, the state of the art in Class-Oriented Programming has been to define interfaces for everything, and then define classes that implement those interfaces, and then use the interface to type functions and methods. A Trait in Rust or a Protocol in Clojure just knocks out the middle man, the unnecessary and unwanted class. What's left is still OO, you can get rid of the class and all of it's baggage and still have plenty of OO left

No, what you're seeing is the evolution of languages away from OO. It is a direct result of the criticism applied to the OO paradigm, and traditionally OO languages recognising its shortcomings, thus evolving other paradigms or practices which bypass the OO model. All these languages are multi-paradigm in essence now. A trait effectively is an alternate concept from an object. It defines functions interface and implementation separately from the datatype. You can have a language with traits yet without objects, such as Clojure/Script. Such a language is not OOP. You can't take away the concept of objects and still be object oriented. This is just support for type polymorphism, and it's ortgogonal to objects.

I think you might be the one with a circular definition of OO. Because you see things in languages that have support for OOP, does not mean all their features are part of the OOP paradigm.

Take Java, remove its support for interfaces, now ask yourself if it still supports object oriented programming? Yes? Why?

At least, this is my taxonomy. But I feel it is also the most common taxonomy in use. And I also feel it is a more useful taxonomy. Things are more granular, more specific. And within this taxonomy, the criticism against OOP is well founded, and more convincing. And it makes sense then that Rust and Haskell and Clojure/Script do not advertise support for OOP. It makes sense why Java, which lacks Traits, is still OOP, etc.

Just my 2 cents.

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3 comments · 1 top-level

likeclockwork7y ago· 2 in thread

I am not saying that traits/protocols/interfaces/typeclasses are necessary for OO, I am saying that they are sufficient.

The object-like construct in Clojure is an instance of a record or a type that implements a protocol. (A deftyped type can even contain mutable fields!) It doesn't matter where the methods live, they apply only to objects that implement the protocol. That's behavior and data bundled together. As far as I am concerned that is an object. A trait is just a different expression of an object from an instance of a class. The interface being defined separately changes nothing; interfaces/traits/typeclasses offer different advantages than subtype polymorphism and inheritance hierarchies.

Would you say CLOS isn't OO?

A trait isn't an object and neither is a class. An instance of a data type that implements a trait is as much an object as an instance of a class.

Rust, Haskell, and Clojure don't advertise support for OOP because in the common taxonomy an object is defined as "an instance of a class".

> Clojure/Script records don't have their methods following them around. You can define the functions for the protocol in another namespace, and then you have to require them separately. They don't tag along with the record.

> Again, the call is made to the protocol functions. Simply importing the record does not make these functions exist within your namespace, you need to require them. And these functions are not scoped within the record. They don't see the fields, they need to access them through the record, like any other function would. Nothing is special about these functions. They're just functions that know how to do something to a concrete datatype.

1. Nothing is special about methods in "OOP" languages either, aside from the dot operator and implicit this. There are object systems that have neither.

2. You have made a factual error here. An implemention of a protocol on a record or a deftyped type(is there a proper non-generic name for this?) DOES have implicit access to the fields of the record or type.

    (defprotocol Container
      (inventory [this])
      (add [this thing]))
    
    (defrecord Box [contents]
      Container
      (inventory [this] contents)
      (add [this thing]
        (update this :contents conj thing)))
    
    boot.user=> (-> (->Box [1 2 3])
                    (add 4)
                    (inventory))
    ;; => [1 2 3 4]

The protocol method clearly has access to the contents field of the record, scoped by the record definition. The 'this' argument is a convenience to allow reconstituting the immutable object for return. You could just as easily have been forced to call the constructor again in order to reconstitute the object. If the record contained an atom it would happily carry around mutable state and there'd be no need to reconstitute anything.

Building on my previous example:

    (deftype MutableBox [^{:volatile-mutable true} contents]
      Container
      (inventory [this] contents)
      (add [this thing]
        (set! contents (conj contents thing))))
    boot.user=> (let [b (->MutableBox [1 2 3])]
                  (add b 4)
                  (inventory b))
    ;; => [1 2 3 4]

A type with mutable state, its fields in scope. This isn't even used.

You're correct that the call IS made to the protocol method. And yes, not having the protocol in scope prevents from calling the object's methods. One might even say that methods you don't know about and thus can't refer to are encapsulated. It's an extremely flexible object system--one that eschews mutable state and works well with a functional style and prefix syntax--but it's still an object system.

Object isn't a keyword in any of the languages we've mentioned. But we know how to find them and what they are. I don't understand why you can't see this one.

didibusOP7y ago

> The protocol method clearly has access to the contents field of the record, scoped by the record definition.

Thank you for pointing this out. I have learned something today. I didn't know that protocols implemented inline within the deftype and defrecord macros were actually given direct access to the fields. And even more surprising to me, that mutable fields on deftype are actually made package restricted. Well then, I have to concede it to you, even within my definition of OOP, deftype is now an equivalent construct to my concept of objects. Those methods are no longer trait like, they're full blown object methods, with special privileges, and tight coupling to the mutable data fields. They can not be defined separately to the type, and a type can not be extended outside its definition to support such methods.

> I am not saying that traits/protocols/interfaces/typeclasses are necessary for OO, I am saying that they are sufficient. > Object isn't a keyword in any of the languages we've mentioned. But we know how to find them and what they are. I don't understand why you can't see this one.

So how would you define OO? I get it your are in the camp that equal polymorphism to OO? And by the way, I do see it. Clojure/Script has object-based constructs. If you think of the more general sense for object, which is identity + attributes, records fit the bill. This is defined here https://en.wikipedia.org/wiki/Object_(computer_science)#Obje.... Now, I also agree with you, it even has a construct that groups data and behavior together in the form of deftype with mutable fields. So at this point, it has support for OOP.

What I'm really arguing is just a taxonomy. I see three distinct characteristics. The grouping of data and behavior together behind an object (OO). The ability to dispatch to different implementations of a procedure based on the datatype (type polymorphism). And the ability to inherit behavior from the behavior of an associated parent (inheritance). And this is my preferred taxonomy.

In that sense, prior to me learning about deftype with mutable fields, I saw Clojure/Script as supporting type polymorphism using either protocols or multi-methods. And inheritance through multi-methods. But I did not see anything to group data and behavior together behind an object. Thus I did not consider it had support for OO.

I know some people say polymorphism alone is the essence of OO. Thus Haskell, Rust, Clojure/Scipt, Go, PureScript, and others are all OO languages. I don't know though, I feel the average dev doesn't think of it that way.

Other people think of OO as the bundling of data and behavior, and that seemed much more reasonable to me. This is how the Gang of Four book defines OO for example. And this is how I like to think of it also.

But, after this conversation, I wonder if I don't prefer the definition from the wiki link I shared. Where OOP is the combination of all three. A single construct which groups data and behavior, and allows polymorphism as well as inheritance. And this is what is known as an object, and all three must be present to be considered OOP. With this definition, I think Clojure/Script wouldn't fit as OOP. Since, and tell me otherwise, deftype doesn't support inheritance. And multi-methods don't group data and behavior.

likeclockwork7y ago

> So how would you define OO? I get it your are in the camp that equal polymorphism to OO? And by the way, I do see it. Clojure/Script has object-based constructs. If you think of the more general sense for object, which is identity + attributes, records fit the bill. This is defined here https://en.wikipedia.org/wiki/Object_(computer_science)#Obje.... Now, I also agree with you, it even has a construct that groups data and behavior together in the form of deftype with mutable fields. So at this point, it has support for OOP.

> I know some people say polymorphism alone is the essence of OO. Thus Haskell, Rust, Clojure/Scipt, Go, PureScript, and others are all OO languages. I don't know though, I feel the average dev doesn't think of it that way.

I don't think that polymorphism alone is sufficient to be considered OO. I think it's important to recognize you can do OOP without much language support, people even do OOP in C. There's probably someone doing OOP in assembly somewhere.

> But, after this conversation, I wonder if I don't prefer the definition from the wiki link I shared. Where OOP is the combination of all three. A single construct which groups data and behavior, and allows polymorphism as well as inheritance. And this is what is known as an object, and all three must be present to be considered OOP. With this definition, I think Clojure/Script wouldn't fit as OOP. Since, and tell me otherwise, deftype doesn't support inheritance. And multi-methods don't group data and behavior.

Lets work with your definition..

You concede that all of those constructs group data and behavior, since they let you define a type's methods in a manner that has access to that type's internal implementation. You concede that they allow polymorphism because you can substitute any type that implements the trait/protocol/interface/typeclass. I don't think subclass inheritance is necessary to OO because it's there as a means of expressing type polymorphism and in the class-bases languages it was for the longest time the only way of expressing type polymorphism. So.. what's the difference between participating in an interface/trait/protocol and inheriting from an abstract class? I don't particularly think there is any (some of these languages even have default implementations, including Haskell), you get subtype polymorphism from either.. so in my view the inheritance requirement is met even without a full-blown class hierarchy or deep prototype chain.

> Those methods are no longer trait like, they're full blown object methods, with special privileges, and tight coupling to the mutable data fields. They can not be defined separately to the type, and a type can not be extended outside its definition to support such methods.

All of the other constructs work the same way, even typeclasses in Haskell. Trait implementations in Rust can have privileged access to private fields. I assume it's the same with Go interfaces. And in Haskell you can't destructure or even construct a type if you don't have access to its constructor--so if you don't export the constructor from your module.. all your fields are private. But you can export a function that constructs the type. You can export the typeclasses. You can export accessors for public fields, and functions to return a modified version of the instance and so forth.

> I know some people say polymorphism alone is the essence of OO. Thus Haskell, Rust, Clojure/Script, Go, PureScript, and others are all OO languages. I don't know though, I feel the average dev doesn't think of it that way.

Well, they're not all OO languages. They all do have language level support for all of the concepts that OOP is made of and you can use them to do Object-Oriented Programming even though some of them are clearly Functional Programming languages. OOP means classes and nothing else in the mind of the average dev. In my opinion it's really just a pattern that you can apply/implement anywhere with more or less support from the language and in sufficiently flexible languages you can even build your own object system and it might even be nice to use. Supporting OOP doesn't make a Functional language not-Functional, or even a multi-paradigm language. No one would call Haskell a multi-paradigm language, yet it has language level support for OOP. Classes and FP don't really mix, but OO in FP works and doesn't have to compromise the FP paradigm. OO isn't something you need to dedicate an entire language to in order to use or benefit from.

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