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;
It works in msvc but as someone pointed out, it was a typo and was meant to be (void*) cast.
This warning is stupid. It's part of the "we reserve the right to change the size of function pointers some day so that we can haz closures, so you can't assume that function pointers and data pointers are the same size m'kay?" silliness. And it is silly: because the C and C++ committees will never be able to change the size of function pointers, not backwards-compatibly. It's not that I don't wish they could. It's that they can't.
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
res.fn = (void *)fn;
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.
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.