Here is examples, recursion stops when `__VA_OPT__` will not expands
(`__VA_ARGS__` empty), In case on infitine recursion there are impl-defined
limit

implementation and discurssion here:
https://github.com/llvm/llvm-project/pull/65851


пт, 10 нояб. 2023 г. в 16:37, Andrey Semashev via Std-Proposals <
std-proposals_at_[hidden]>:

> On 11/10/23 15:22, Nikl Kelbon via Std-Proposals wrote:
> > Hi all, I would like to propose a minor addition to the preprocessor,
> > that has the potencial to significantly simplify writing and reading
> > macros, give new features that were not there.
> >
> > I propose a special token '__THIS_MACRO__'(similar to '__VA_ARGS__' and
> > '__VA_OPT__' ), which will add the possibility to write recursive macros.
> >
> > Simple example:
> >
> > #define fold_right( op , head , ...) \
> > ( head __VA_OPT__ ( op __THIS_MACRO__(op, __VA_ARGS__ )))
> > /* expands to (1 + (2 + (3))) */
> > int i = fold_right(+ , 1 , 2 , 3 );
> >
> >
> > This can be used in many different scenarios,
> > * declaring enums with enum info(like names, count, etc)
> > * boost describe struct
> > * ... more examples in 'pdf' ...
>
> When does the recursion stop? IOW, what one is supposed to write in the
> macro definition to stop the recursion at a certain point?
>
> --
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