Thanks Stefan. 

That's great help and for now will allow me to provide working C#
support to Emacs 26 users, while I work out what to do with our
troublesome usage of internal cc-mode functions. I really appreciate it.
I picked up this project as a community service when editing C# stopped
working sometime in Emacs 24, and it would be pretty daft to simply give
up on it now. :)
--
Regards
Jostein Kjønigsen


On Mon, Mar 12, 2018, at 11:40 PM, Stefan Monnier wrote:
>> Is there any way for package to know how many mandatory arguments a
>> function has, to be able to branch out for compatibility reasons?
> 
> The way I recommend is:
> 
>     (condition-case nil
>         (call1 ...)
>       (wrong-number-of-arguments
>       (call2 ...)))
> 
> 
> -- Stefan
> 
>