> This is not a thing in C. Linus Torvalds can add a function F that operates on the internals of both FILE and DIR at the same time, for example, and suddenly it's less clear who "owns" F and which one is the object.
It isn’t a thing in a C++ either if one makes all the fields public or if one uses friend.
Member accessibility is not essential to the idea of OOP, since there are OOP languages which don’t have it, or in which it is merely a convention, or something which can be overridden-and a person can use an OOP language which has it yet fail to use it.
So, I don’t think “C lacks private members” is a good argument against C being “OOP”. Especially when C actually has the moral equivalent of “private” given APIs can be based on opaque pointers, so your compilation unit has no idea what the fields or layout of some structure controlled by another is.
But it is a thing in OOP. That's the point. C++ is multiparadigm. All the OOP gurus will tell you that objects shouldn't expose their internal data, only methods.
That's why the so-called encapsulation is constantly brought up. People telling you C is OOP will say "FILE is an object, the FILE struct + fopen/fclose/fwrite constitute an object, FILE is opaque, we can only interact with its internals through the public methods". "DIR is an object, ...". And so on.
And the problem is that when the Linux C API exposes a function that takes both a FILE and a DIR, and operates on both their internals, your whole idea of OOP-ness shatters because a method can only belong to a single object, by definition.
> And the problem is that when the Linux C API exposes a function that takes both a FILE and a DIR, and operates on both their internals, your whole idea of OOP-ness shatters because a method can only belong to a single object, by definition.
You can do the same in Smalltalk though-create a utility class containing a method which operates on one instance of each class, and create accessors to expose all their internals. If the ability to do that means C isn’t an OO language, then Smalltalk isn’t an OO language either. And if Smalltalk isn’t an OO language, then OO languages don’t exist.
I'm confused by the sudden digression to Smalltalk. I was talking about C. I'll restate my point.
Take the GNU C library. You don't own it, you just use it. It exposes some types (FILE, DIR), and some functions that use these types.
Then, some people look at this API and proclaim that FILE and DIR are (conceptually) objects, and that there's no difference to having 2 C++ classes, it's just syntactic sugar. And that, therefore, C is OOP (or at least the design of libc).
So now I ask - to which of the so-called objects does F(const char, FILE, DIR) belong?
The answer is whatever you want it to be, because they're only objects in your mind, and you can imagine that F belongs to FILE, or to const char, or to all of them, or FILE/DIR stop being objects, and so on. Without syntax for objects (either explicit or implicit by convention), it's up to your imagination to decide what are the objects in your program. But if imagination is the criteria for OO-ness, then any programming language can be declared OO.
OO is such a fuzzy concept that almost every feature and "pillar" is optional except objects. My point is that if a language doesn't have a syntax for objects then it's not actually OO.
You can, of course, apply an OO mindset to your C program, but you can apply an OO mindset to anything Turing-complete, from Haskell to SQL and x86 assembly, so that's not saying much. If you approach everything with an OO mindset, that doesn't mean everything is OO.
> I'm confused by the sudden digression to Smalltalk. I was talking about C. I'll restate my point.
You are arguing "C cannot be an OO language because it lets you do X, and an OO language won't let you do X." My counterargument is "Smalltalk lets you do X, but everyone agrees that Smalltalk is an OO language; hence, you claim that if a language lets you do X it can't be an OO language must be false".
> So now I ask - to which of the so-called objects does F(const char, FILE, DIR) belong? The answer is whatever you want it to be, because they're only objects in your mind, and you can imagine that F belongs to FILE, or to const char, or to all of them, or FILE/DIR stop being objects, and so on.
If a language permits methods/functions which do not belong to any class, does that mean it can't be OO?
A class-less method/function is equivalent to a single-method utility class. A language can't be OO if it lets you create a utility class?
> Without syntax for objects (either explicit or implicit by convention), it's up to your imagination to decide what are the objects in your program.
In the above program, why isn't `counter` an object? Assumably "privateData" is just a pointer to an int, but for all you know, the Counter value is actually stored as EBCDIC Roman numerals.
> My point is that if a language doesn't have a syntax for objects then it's not actually OO.
C in itself has no concept of an "object". But, there are certain conventions you can adopt in C code which make something an "object". My code above is one example of such a convention, there are others – for example, Microsoft COM (an object is a struct whose first member is a pointer to a struct of function pointers, and the remainder of the struct is private to the implementing class).
^ This, 100%. GTk's GObject type system which powers the entire GNOME stack is a similar object-oriented C type system with a virtual table pointer as the first member of an object, similar to Microsoft COM and C++.
The entire Objective-C runtime which is what powers the OO core of the language was also written with a similar purely C type system... It's just a small compiler layer on top...
> In the above program, why isn't `counter` an object?
> C in itself has no concept of an "object".
You answered your own question.
Without syntax to say "this is an object", you can take literally ANYTHING Turing-complete, mentally group data+functions and then claim "it looks like an object, therefore it is an object, why wouldn't it be an object". "Excel is OO", "Dwarf fortress is OO", "x86 assembly is OO", "pen and paper is OO".
Well, if everything is OO then nothing is OO, you've made it into a meaningless concept.
I suggest we stick to reality. The most basic requirement for a language to be OO is to have some explicit or implicit syntax for objects. That seems to reasonably partition languages into OO and non-OO.
> You are arguing "C cannot be an OO language because it lets you do X, and an OO language won't let you do X."
I'm arguing no such thing, and I never said such a thing. Would appreciate if you didn't put words in my mouth.
I'll ask again.
In my concrete example, given that FILE and DIR were classified as objects, to which of the so-called objects does F(const char*, FILE, DIR) belong? Possible answers: 1. FILE 2. DIR 3. None of them 4. Both of them 5. They stop being objects 6. New objects are created, and those own F 7.Something else
Pick one. I will then pick any other option and argue that, in my opinion, my chosen answer is the correct one. And then it's suddenly a matter of opinion rather than a matter of fact, you won't be able to prove I am wrong, just like I won't be able to prove I'm right. So much for imaginary objects.
EDIT
> In the above program, why isn't `counter` an object?
To drive my point home, why is it an object? Just because you see an object? All I see is a struct containing 5 pointers. Oh, some are function pointers? What's the difference, it's still just a struct containing 5 pointers. You consider it an object, I don't consider it an object, and none of us is wrong.
However, an instance of a C++ class containing members and methods is unambiguously an object because the syntax clearly bound them together. Plus, you can do OO things with this object, which further reinforces the idea that it is an object.
#include "oo.h"
DEFINE_CLASS(Counter,
int METHOD(Counter,getValue,NO_ARGS);,
void METHOD(Counter,increment,NO_ARGS);,
void METHOD(Counter,decrement,NO_ARGS);,
void METHOD(Counter,multiplyThenAdd,(int multiplyBy, int add));
);
That's valid C, given appropriate preprocessor macro definitions.
It is a bit ugly, due to the limitations of the C preprocessor.
(Maybe someone else can do better than me.)
If C had a more powerful preprocessor, but was otherwise unchanged, the syntax could be a lot nicer.
The DEFINE_CLASS() macro expands to declare a function:
Counter* newCounter(void);
Why isn't the return value of that function an object?
The above macros are admitttedly very hairy. If C had a better preprocessor, but was otherwise unchanged, they could look a lot nicer.
> I never said such a thing. Would appreciate if you didn't put words in my mouth.
A normal part of dialogue is, "I'm going to repeat your point back to you in my own words, and you can either agree with my restating of it, or point out at which point I've misunderstood you". That's what I was doing. "Would appreciate if you didn't put words in my mouth" is unnecessary hostility.
> In my concrete example, given that FILE and DIR were classified as objects, to which of the so-called objects does F(const char*, FILE, DIR) belong?
Take any language which you agree is "OO". Add one new feature (if it isn't already there): functions/methods which don't belong to any class/object. Now the function you are talking about is possible in that language. Did the language thereby suddenly cease to be OO when we added that feature? Most people would disagree with "Yes". But if "No", what is the actual difference between C and that language?
> > In my concrete example, given that FILE and DIR were classified as objects, to which of the so-called objects does F(const char*, FILE, DIR) belong?
> Take any language which you agree is "OO". ...
A normal part of dialogue is answering the other person's questions. I asked the same question point blank several times, and you keep refusing to answer. Once you answer the question, then we can discuss your hypothetical scenarios about other languages. I believe I stated my question quite clearly.
> Why isn't the return value of that function an object?
> In my concrete example, given that FILE and DIR were classified as objects, to which of the so-called objects does F(const char*, FILE, DIR) belong? Possible answers: 1. FILE 2. DIR 3. None of them 4. Both of them 5. They stop being objects 6. New objects are created, and those own F 7.Something else
I don't think your question necessarily has an answer, but if I have to pick, I'd say (3). F is a classless method; FILE and DIR are classes; as a classless method, F cannot belong to any class, so it can't belong to FILE or DIR.
If the function was F(FILE, const char*, DIR) then F might be a method of FILE instead, if the code base is following the "this is first argument" convention.
> I don't think your question necessarily has an answer,
And why is that? Are objects and OOP not clearly defined? If you proclaim FILE and DIR to be classes, should it not be extremely clear what are their methods?
That's the problem right there, as I said it repeatedly. In C++, objects can be identified unambiguously.
Whereas in C, if you keep insisting it's OOP, the answer is whatever you want it to be. "FILE is an object, and I'll handwave away all inconvenient details that get in the way of my perception of FILE as an object". Sorry, I expect a higher level of rigour.
> F is a classless method
> FILE and DIR are classes
> If the function was F(FILE, const char, DIR) then F might be a method of FILE instead, if the code base is following the "this is first argument" convention.
The C standard library doesn't seem to follows such a convention. For example:
> fread(void , size_t, size_t, FILE );
> fgets(char, int, FILE );
> fseek(FILE , long int, int);
If FILE is a class, is fgets a method of this class? If fgets is a method of FILE, why is F in my example not a method of FILE too?
It isn’t a thing in a C++ either if one makes all the fields public or if one uses friend.
Member accessibility is not essential to the idea of OOP, since there are OOP languages which don’t have it, or in which it is merely a convention, or something which can be overridden-and a person can use an OOP language which has it yet fail to use it.
So, I don’t think “C lacks private members” is a good argument against C being “OOP”. Especially when C actually has the moral equivalent of “private” given APIs can be based on opaque pointers, so your compilation unit has no idea what the fields or layout of some structure controlled by another is.