Re: [PATCH] regex: use C99-style array arg syntax

[Bruno Haible]

Hi Paul,

Thanks for the explanations.

> any of the access modes 'read', 'write', 
> 'read_write', 'none' are incorrect for some valid and reasonable regexec 
> calls.

So, to make the __access__ attribute [1] really consistent, they would need to
add a fifth access-mode 'any', that would not restrict the access pattern.

>    void g (int n, int a[n]) { }
>    void h (int n, int a[static n]) { }

So, the 'g' syntax is a somewhat broken language feature, since the compiler
can use it for warnings but not for optimizations.

And the essential difference between 'g' and 'h' is that g accepts a NULL
argument, whereas 'h' doesn't.

How about this comment for _REGEX_NELTS, then?

/* Specify the number of elements of a function's array parameter,
   as in 'int f (int n, int arr[_REGEX_NELTS (n)]);'
   if arr may be NULL,
   or    'int f (int n, int arr[_REGEX_NELTS (static n)]);'
   if arr must be non-NULL.  */

Bruno

[1] 
https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/Common-Function-Attributes.html