Re: Type-safe typecasts

[Paul Eggert <eggert@cs.ucla.edu>]

On 4/6/21 12:18 AM, Marc Nieper-Wißkirchen wrote:
> So what I have in mind are macros that do a type conversion from A to B and
> that signal an error on modern compilers if the input is not of type A. For
> this, the C11 construct _Generic can be used.

Not sure it's worth the aggravation. Most of the time, the type you're 
converting to void * is obvious from context. (However, I guess I 
wouldn't object in code that I don't have to look at myself. :-)

By the way, the snippet you gave is not portable C code, as it assumes 
that 'void *' and 'struct foo *' have the same machine representation. 
This is not necessarily true on (admittedly now-rare) machines that have 
different flavors of pointers. I suspect the main problem here is either 
in the calling code, or in the API for gl_list_iterator_next: if it 
returned a possibly-null value of type 'const void *' instead of storing 
the result through a 'const void **' pointer, the calling code wouldn't 
have gotten into this portability mess.