On 2023-12-04 13:51, Jakub Jelinek wrote:
Why? The syntax doesn't seem to be something unexpected, and as C doesn't have lambdas, one can use the nested functions instead. The only problem is if you need to pass function pointers somewhere else (and target doesn't have function descriptors or something similar), if it is only done to make code more readable compared to say use of macros, I think the nested functions are better, one doesn't have to worry about multiple evaluations of argument side-effects etc. And if everything is inlined and SRA optimized, there is no extra cost. The problem of passing it as a function pointer to other functions is common with C++, only lambdas which don't capture anything actually can be convertible to function pointer, for anything else you need a template and instantiate it for a particular lambda (which is something you can't do in C).
I think from a language standpoint, the general idea that nested functions are just any functions inside functions (which is how the C nested functions essentially behave) is too broad and they should be restricted to minimal implementations that, e.g. don't have side-effects or if they do, there's explicit syntactic sugar to make it clearer.
If (like Martin stated earlier), nested functions are in fact going to enter the C standard in future then maybe this discussion is moot and we probably are better off implementing descriptor support for C to replace the on-stack trampolines instead of adding -Werror=trampolines in a hurry.
Thanks, Sid
