alt Hacker NewsOh, I definitely agree with some of your other points, just not the one I argued against.
BTW, I would also contest that your version is faster at runtime. Your data always allocated on the heap. Depending on the size of the data, std::function can utilize small function optimization and store everything in place. This means there is no allocation when setting the callback and also better cache locality when calling it. Don't make performance claims without benchmarking!
Similarly, the smaller memory footprint is not as clear cut: with small function optimization there might be hardly a difference. In some cases, std::function might even be smaller. (Don't forget about memory allocation overhead!)
The only point I will absolutely give you is compilation times. But even there I'm not sure if std::function is your bottleneck. Have you actually measured?
That's a fair point. I just looked and out of 35 uses of MkFunc0 only about 3 (related to running a thread) allocate the args.
All others use a pointer to an object that exists anyway. For example, I have a class MyWindow with a button. A click callback would have MyWindow* as an argument because that's the data needed to perform that action. That's the case for all UI widgets and they are majority uses of callbacks.
I could try to get cheeky and implement similar optimization as Func0Fat where I would have inline buffer on N bytes and use it as a backing storage for the struct. But see above for why it's not needed.
As to benchmarking: while I don't disagree that benchmarking is useful, it's not the ace card argument you think it is.
I didn't do any benchmarks and I do no plan to.
Because benchmarking takes time, which I could use writing features.
And because I know things.
I know things because I've been programming, learning, benchmarking for 30 years.
I know that using 16 bytes instead of 64 bytes is faster. And I know that likely it won't be captured by a microbenchmark.
And even if it was, the difference would be miniscule.
So you would say "pfft, I told you it was not worth it for a few nanoseconds".
But I know that if I do many optimizations like that, it'll add up even if each individual optimization seems not worth it.
And that's why SumatraPDF can do PDF, ePub, mobi, cbz/cbr and uses less resources that Windows' start menu.