I think none of these points are demonstrated in the post hence I fail to visualize it

Also I copy pasted the code from the post and I got this:

test.cpp:70:14: error: assigning to 'void ' from 'func0Ptr' (aka 'void ()(void *)') converts between void pointer and function pointer 70 | res.fn = (func0Ptr)fn;

Thanks, fixed.

It works in msvc but as someone pointed out, it was a typo and was meant to be (void*) cast.

It’s not a warning, it’s a compile time error and I am not even using -Wall -Werror

I also believe there are platforms where a function pointer and a data pointer are not the same but idk about such esoteric platforms first hand (seems Itanium had that: https://stackoverflow.com/questions/36645660/why-cant-i-cast...)

Though my point was only that this code will not compile as is with whatever clang Apple ships*

I am not really sure how to get it to compile tbqh

Some further research ( https://www.kdab.com/how-to-cast-a-function-pointer-to-a-voi...) suggest it should be done like so:

> auto fptr = &f; void a = reinterpret_cast<void &>(fptr);

edit: I tried with GCC 15 and that compiled successfully

FWIW, POSIX practically requires void otr and function otr inter-convertibility hence the support from GCC.

Not practically, but literally:

  Note that conversion from a void * pointer to a function
  pointer as in:

    fptr = (int (*)(int))dlsym(handle, "my_function");

  is not defined by the ISO C standard. This standard
  requires this conversion to work correctly on conforming
  implementations.

I remembered the dlsym requirement, I wasn't sure it was de-jure.

It should just be

    res.fn = (void *)fn;

`res.fn` is of type `void *`, so that's what the code should be casting to. Casting to `func0Ptr` there seems to just be a mistake. Some compilers may allow the resulting function pointer to then implicitly convert to `void *`, but it's not valid in standard C++, hence the error.

Separately from that, if you enable -Wpedantic, you can get a warning for conversions between function and data pointers even if they do use an explicit cast, but that's not the default.

You can't just keep claiming these things without providing evidence. How much faster? How much smaller? These claims are meaningless without numbers to back it up.

I think the one key downside for std::function+lambda which resonated with me was bad ergonomics during debugging.

My unanswered question on this from 8 years ago:

https://stackoverflow.com/questions/41385439/named-c-lambdas...

If there was a way to name lambdas for debug purposes then all other downsides would be irrelevant (for most usual use cases of using callbacks).

> If there was a way to name lambdas for debug purposes then all other downsides would be irrelevant (for most usual use cases of using callbacks).

Instead of fully avoiding lambdas, you can use inheritance to give them a name: https://godbolt.org/z/YTMo6ed8T

Sadly that'll only work for captureless lambdas, however.

Your Func thing is better than std::function the same way a hammer is better than a drill press... ie it's not better because it's not the same thing at all. Yes the hammer can do some of the same things, at a lower complexity, but it can't do all the same things.

What I'm trying to say is being better than x means you can do all the same things as x better. Your thing is not better, it is just different.

None of the arguments on this list seem convincing. The only one that makes sense was the argument that it helps identify the source of a crash.

How much smaller is it? Does it reduce the binary size and RAM usage by just 100 bytes?

Is it actually faster?

How much faster does it compile? 2ms faster?

I didn't write that article to convince anybody.

I wrote it to share my implementation and my experience with it.

SumatraPDF compiles fast (relative to other C++ software) and is smaller, faster and uses less resources that other software.

Is it because I wrote Func0 and Func1 to replace std::function? No.

Is it because I made hundreds decisions like that? Yes.

You're not wrong that performance wins are miniscule.

What you don't understand is that eternal vigilance is the price of liberty. And small, fast software.

This is a valid point missed by many today. The mantra of don't optimise early is often used as an excuse to not optimise at all, and so you end up with a lot of minor choices scattered throughout the code with all suck a tiny bit of performance out of the system. Fixing any of these is also considered to be worthless, as the improvement from any one change is miniscule. But added up, they become noticeable.

In my experience performance comes from constant vigilance and using every opportunity to choose the performant way of implementing something.

Silly bottlenecks are half of the perf story in my experience. The other half are a billion tiny details.

But do you have actual proof for your first claim? Isn't it possible that the "constant vigilance" is optimizing that ~10% that doesn't really matter in the end?

Yes.

For example C++ can shoehorn you to a style of programming where 50% of time is spent in allocations and deallocations if your code is otherwise optimal.

The only way to get that back is not to use stl containers in ”typical patterns” but to write your own containers up to a point.

If you didn’t do that, youd see in the profiler that heap operations take 50% of time but there is no obvious hotspot.

This is not proof. What you said is not incorrect, but it doesn't prove that your software is fast because you applied small optimizations everywhere.

> Smaller size at runtime (uses less memory).

Yours is smaller (in terms of sizeof), because std::function employs small-buffer optimization (SBO). That is if the user data fits into a specific size, then it's stored inline the std::function, instead of getting heap allocated. Yours need heap allocation for the ones that take data.

Whether yours win or lose on using less memory heavily depends on your typical closure sizes.

> Faster at runtime

Benchmark, please.