[sligor]

Not an array, a struct is ok, and in C99 style it is very well readable.

For example Linux Kernel style is:

  static const struct file_operations fops = {
        .open    = my_open,
        .release = my_release,
        .read    = my_read,
        .write   = my_write
  };

that's all, very straightforward. Also there is no need to prefix the function name with &

[mistrial9]

PP (parent post) here - yes, several variations available in C99; I haven't tried to retrieve my examples yet. (I used this commercially in the 90s)

[ncmncm]

This pattern goes back to pre-Version-7 UNIX kernels, with only minor syntactic updates. That it long predates OO demonstrates it is not OO. That does not make it any less effective, or less useful.

[adrian_b]

It does not predate OO.

The first OO language, SIMULA-67 became public knowledge before the start of even the PDP-7 UNIX, which is extremely unlikely to have used such a pattern, which probably appeared only when UNIX was rewritten in C, starting in 1973.

Even Smalltalk-72 predated the C-version of UNIX.

However, it is likely that this pattern was chosen in UNIX independently of the previous OO languages.

[pjmlp]

Also what many usually forget, C++ was also born on the same building as UNIX.

Hence why C++ got so fast adopted across UNIXes and C compiler vendors on other platforms.

[ncmncm]

That was not the reason.

But it was the reason that C, as standardized, adopted several C++ innovations first.

[pjmlp]

It was definitly the reason, by 1992 it was impossible to buy a C compiler that also did not had a C++ one in the box.

Also why Apple moved from Object Pascal to C++ on MPW.

[ncmncm]

None of those C or C++ compilers came from Bell Labs, or were on UNIX tapes from Bell Labs. I used Cfront on Apollo machines in the '80s. Effectively nobody was using Cfront by 1992.

Apple, particularly, was not strongly influenced by Bell Labs or UNIX. Apple A/UX–a UNIX for Macintosh, a niche product from that period–shipped without a C++ compiler. MPW in 1992 shipped without a C++ compiler.

[mst]

To a great extent, the difference between "a data structure plus a dispatch table" and "an object" is primarily in how you squint.

It's certainly a form of polymorphism.

[rurban]

It's a measurable difference. OO in C++ must use double indirect vtable method calls, whilst this OO in C uses only one indirection. It's measurably faster. Objects are a bit larger though, cloning is a bit more expensive, but method calls are much faster and much easier to cache.

[aaaaaaaaaaab]

I think you're misinterpreting GP's code. It is a vtable, hence the static const. There would be a pointer in each struct "instance" to this static vtable, thus the same double indirection would occcur as in C++.

[mst]

Plus this was a discussion about conceptual models and "what counts as OO", not the specific details and optimisation possibilities of the implementation.

[rurban]

OP mimic'd C++ vtables. But in C you can do better and inline them. I mostly inline them for performance reasons.

[jcelerier]

> That it long predates OO demonstrates it is not OO.

This does not make any sense. People did not wait until someone gave a name to the rule-of-three to use it, and that does not make these uses any less rule-of-three than the ones that occured post-naming.