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OOP in C

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Re: OOP in C

#41

Post by cihangir »

zabzonk wrote: post #13
twawaaay wrote: post #9

Earlier quoted context omitted.

Hi. For background, I have been writing professional OOP code in ANSI C. Yes, Structures in C can be used as classes. And yes, this includes polymorphism. My solution was to put a callback in the structure that would point to the implementation that was polymorphic. This allowed me to pass the struct around and then call the specific implementation at the right time. When you write OOP in C you do not need to make it…

please post an example of what such a callback would look like

Linux kernel code makes heavy use of object-oriented design patterns [0]. It's not the best of its kind, but still provides a reasonable example of how OOP can be achieved in C: https://gist.github.com/cakturk/cd75d0ca588151c86d641cb6d5a1...

[0] https://lwn.net/Articles/444910/

Re: OOP in C

#42

Post by [deleted] »

antirez wrote: post #12

C required the simplest form of OOP, but who standardizes it decided to deny the feature to the language: the ability to have callable structure methods (function pointers) with explicit "self" pointer. Not even constructors/destructors. After all it's C, and you can write list->init() and list->free(). This simple form to bind data and the functions operating on such data would make many codebases better.

[deleted]

Re: OOP in C

#43

Post by isityouyesitsme »

lll-o-lll wrote: post #19
throw_m239339 wrote: post #14

Earlier quoted context omitted.

> Please, try not to be too dismissive to the things you do not understand. I never said it's impossible to do method polymorphism in C, I said nowhere in that article method polymorphism is implemented. You obviously did not read what I wrote at first place, only saw what you wanted to see to make some kind of (bad) rebuttal without a single concrete implementation as an example. Of course it's possible to implement…

Yes, the article is terrible as it does not show any polymorphism. Also, yes, doing genuine polymorphic OO in C ends up horrible because you invent a new language. (Source: many years working on a truely evil code-base of OO C. Originally the work of one twisted genius. Brilliant, but evil). OO was just a failed paradigm anyway, I’m amazed anyone would try and shoe-horn it into C in the modern day.

I don't think OOP has failed at all. It has become the foundation of all reusable code in every language. What failed was the idea that internal state can be managed and shared with derived classes.

The key to OOP is extracting the idea of types/concepts into interfaces that may have different implementations.

You don't even need a language that supports polymorphism as a first-class concept in order to do this, though it is certainly much safer. Python chooses duck typing, modern C++ uses "concepts," etc. You can do SOLID under any of this. Some languages or frameworks take it too far and think of everything as an instance of a base object, for no great reason.

I guess a summary of my thesis is that the "L" in SOLID is what makes an architecture OOP.

Re: OOP in C

#44

Post by zozbot234 »

alerighi wrote: post #40
Vogtinator wrote: post #33

Earlier quoted context omitted.

That wouldn't actually help much. In the case that there is no inheritance, using a function pointer has unnecessary overhead (pointer storage, indirect call, additional parameter). In the case of inheritance, the pointer type differs and thus the function pointer type wouldn't be compatible either.

Inheritance is nowadays almost considered a bad practice, in fact newer languages, such as Rust, doesn't support it, and in languages that has it (Java, C#, etc) nowadays they always tell you to prefer composition over inheritance. > using a function pointer has unnecessary overhead This is true, it's inefficient. But for a lot of application, also irrelevant at performance level, and would provide a good abstraction…

AIUI you can implement inheritance as a pattern on top of existential types, using a self-recursive definition trick. Not sure if Rust has full existential types yet, but they're definitely a goal since they're needed e.g. for better async support.

Re: OOP in C

#45

Post by AlbertoGP »

antirez wrote: post #12

C required the simplest form of OOP, but who standardizes it decided to deny the feature to the language: the ability to have callable structure methods (function pointers) with explicit "self" pointer. Not even constructors/destructors. After all it's C, and you can write list->init() and list->free(). This simple form to bind data and the functions operating on such data would make many codebases better.

I made a pre-processor [1] to add similar features to C, and after reading your comment I’m thinking that it would be simple to add a setting/#pragma to do these transformations:

    list->init(); → list->init(list);
    list.init();  → list.init(&list);
[1] https://sentido-labs.com/en/library/cedro/202106171400/#back...

I normally avoid the function pointer overhead, which can be done with _Generic:

    #define append(VEC, START, END) _Generic((VEC), \
      Vec_float*: append_Vec_float, \
      Vec_str*: append_Vec_str, \
      Vec_cstr*: append_Vec_cstr \
      )(VEC, START, END)
https://sentido-labs.com/en/library/cedro/202106171400/#loop...

But list->init(list) might be a simpler solution for most cases, and compatible with C89/C99.

Re: OOP in C

#46

Post by michaelcampbell »

I was surprised no one here mentioned cfront. My first job out of college I would look at the generated C code from my C++ source to see how it would convert some of the the C++ things into C, since I couldn't figure out how to do it myself.

Re: OOP in C

#48

Post by meindnoch »

twawaaay wrote: post #9
throw_m239339 wrote: post #7

[flagged]

Hi. For background, I have been writing professional OOP code in ANSI C. Yes, Structures in C can be used as classes. And yes, this includes polymorphism. My solution was to put a callback in the structure that would point to the implementation that was polymorphic. This allowed me to pass the struct around and then call the specific implementation at the right time. When you write OOP in C you do not need to make it…

>My solution was to put a callback in the structure

I think you mean function pointer. But yeah, that's the usual way to do it, although a bit wasteful in terms of memory compared to a vtable (but needs one less indirection to jump to the method).

Re: OOP in C

#49

Post by throw_m239339 »

BulgarianIdiot wrote: post #31
throw_m239339 wrote: post #7

[flagged]

All you need is a field in the struct to point to your vtable. Please try to think more charitably and not be so aggressive. Even if the author was wrong, which they aren't, doesn't mean they don't have the kernel of a good idea. Charitability is not a tool merely for being nice to others, but being nice to yourself. You learn more this way.

[flagged]
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