But you can't do it in C. __typeof__ is a GNU extension.
> Note that wl_list is not a very safe data structure, in the sense that a programmer need to know exactly how to use it.
You can do it in C++ with template, and it would be type safe.
Yes you can. You just have to provide the type every time you use the macro yourself. You can even create a macro that creates helper “methods” for you.
With that said, I really dislike how common it is for C programmers to just use whatever their compiler's authors felt like adding and still calling it “portable C”. At this point, if you dislike “plain” C so much, you might as well just switch to a subset of C++ or D's “Better C” mode.
#define wl_container_of(ptr, sample, member) \
(void*)((char *)(ptr) + ((char*)(sample) - (char*)(&(sample)->member)))You can do it in C, you just can't do it in the part of C the standards committee has decided to standardize.
I'm not sure what the value is of defining C as standard C when loads of software has shipped for decades using this pattern.
(The C standard explicitly calls this out as a valid way of handling UB.)
But extensions like typeof are different from UB. They have documented behavior, it is just documented by GNU instead of the C standards committee.