What makes a language Object-Oriented?

Question

Since debate without meaningful terms is meaningless, I figured I would point at the elephant in the room and ask: What exactly makes a language \"object-oriented\"? I\'m no

Answer 1

To further what aib said, I would say that a language isn't really object oriented unless the standard libraries that are available are object oriented. The biggest example of this is PHP. Although it supports all the standard object oriented concepts, the fact that such a large percentage of the standard libraries aren't object oriented means that it's almost impossible to write your code in an object oriented way.

It doesn't matter that they are introducing namespaces if all the standard libraries still require you to prefix all your function calls with stuff like mysql_ and pgsql_, when in a language that supported namespaces in the actual API, you could get rid of functions with mysql_ and have just a simple "include system.db.mysql.*" at the top of your file so that it would know where those things came from.

Answer 2

Object: An object is a repository of data. For example, if MyList is a ShoppingList object, MyList might record your shopping list.

Class: A class is a type of object. Many objects of the same class might exist; for instance, MyList and YourList may both be ShoppingList objects.

Method: A procedure or function that operates on an object or a class. A method is associated with a particular class. For instance, addItem might be a method that adds an item to any ShoppingList object. Sometimes a method is associated with a family of classes. For instance, addItem might operate on any List, of which a ShoppingList is just one type.

Inheritance: A class may inherit properties from a more general class. For example, the ShoppingList class inherits from the List class the property of storing a sequence of items.

Polymorphism: The ability to have one method call work on several different classes of objects, even if those classes need different implementations of the method call. For example, one line of code might be able to call the "addItem" method on every kind of List, even though adding an item to a ShoppingList is completely different from adding an item to a ShoppingCart.

Object-Oriented: Each object knows its own class and which methods manipulate objects in that class. Each ShoppingList and each ShoppingCart knows which implementation of addItem applies to it.

In this list, the one thing that truly distinguishes object-oriented languages from procedural languages (C, Fortran, Basic, Pascal) is polymorphism.

Source: https://www.youtube.com/watch?v=mFPmKGIrQs4&list=PL-XXv-cvA_iAlnI-BQr9hjqADPBtujFJd

Answer 3

I am happy to share this with you guys, it was quite interesting and helpful to me. This is an extract from a 1994 Rolling Stone interview where Steve (not a programmer) explains OOP in simple terms.

Jeff Goodell: Would you explain, in simple terms, exactly what object-oriented software is?

Steve Jobs: Objects are like people. They’re living, breathing things that have knowledge inside them about how to do things and have memory inside them so they can remember things. And rather than interacting with them at a very low level, you interact with them at a very high level of abstraction, like we’re doing right here.

Here’s an example: If I’m your laundry object, you can give me your dirty clothes and send me a message that says, “Can you get my clothes laundered, please.” I happen to know where the best laundry place in San Francisco is. And I speak English, and I have dollars in my pockets. So I go out and hail a taxicab and tell the driver to take me to this place in San Francisco. I go get your clothes laundered, I jump back in the cab, I get back here. I give you your clean clothes and say, “Here are your clean clothes.”

You have no idea how I did that. You have no knowledge of the laundry place. Maybe you speak French, and you can’t even hail a taxi. You can’t pay for one, you don’t have dollars in your pocket. Yet, I knew how to do all of that. And you didn’t have to know any of it. All that complexity was hidden inside of me, and we were able to interact at a very high level of abstraction. That’s what objects are. They encapsulate complexity, and the interfaces to that complexity are high level.

Answer 4

Basically Object Oriented really boils down to "message passing"

In a procedural language, I call a function like this :

  f(x)

And the name f is probably bound to a particular block of code at compile time. (Unless this is a procedural language with higher order functions or pointers to functions, but lets ignore that possibility for a second.) So this line of code can only mean one unambiguous thing.

In an object oriented language I pass a message to an object, perhaps like this :

 o.m(x) 

In this case. m is not the name of a block of code, but a "method selector" and which block of code gets called actually depends on the object o in some way. This line of code is more ambiguous or general because it can mean different things in different situations, depending on o.

In the majority of OO languages, the object o has a "class", and the class determines which block of code is called. In a couple of OO languages (most famously, Javascript) o doesn't have a class, but has methods directly attached to it at runtime, or has inherited them from a prototype.

My demarcation is that neither classes nor inheritance are necessary for a language to be OO. But this polymorphic handling of messages is essential.

Although you can fake this with function pointers in say C, that's not sufficient for C to be called an OO language, because you're going to have to implement your own infrastructure. You can do that, and a OO style is possible, but the language hasn't given it to you.

Answer 5

As far as I can tell, the main view of what makes a language "Object Oriented" is supporting the idea of grouping data, and methods that work on that data, which is generally achieved through classes, modules, inheritance, polymorphism, etc.

See this discussion for an overview of what people think (thought?) Object-Orientation means.

As for the "archetypal" OO language - that is indeed Smalltalk, as Kristopher pointed out.

Answer 6

Disregarding the theoretical implications, it seems to be

"Any language that has a keyword called 'class'" :-P