[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.

[pjmlp]

So what? Did you missed the part about compiler vendors?

Those were the ones that cared about C outside UNIX.

Bell Labs also had nothing to say to what happened to their code when they set it free.

And Zortech was one of the first vendors to move away from CFront.

[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.