Re: [Nmh-workers] nmh internals: argument processing

[Lyndon Nerenberg]

On 2013-01-07, at 3:52 PM, Ken Hornstein wrote:

> nmh uses a function called smatch() to parse options.  You give it a
> "struct swit" array, which contains the following members:
> 
>       char *sw;       /* Name of switch */
>       int minchars;   /* Minimum number of characters to match switch name */
> 
> smatch returns an index into the "struct swit" array.  If you've looked at
> nmh code, you've seen plenty of stuff like this (from inc.c):
> 
> static struct swit switches[] = {
> #define AUDSW                      0
>    { "audit audit-file", 0 },
> #define NAUDSW                     1
>    { "noaudit", 0 },
> #define CHGSW                      2
>    { "changecur", 0 },
> #define NCHGSW                     3
>    { "nochangecur", 0 },
> [...]
> 
> So the "fun" part here is that humans have to deal with manually keeping
> these defines matched up to the index into the swit array, and if you add or
> delete switches you have to adjust all of the #define's after your
> change.  This annoys me to no end, and I've been thinking lately: Why I am
> doing this, exactly?  Why isn't the compiler doing it for me?
> 
> It occurs to me that it would be simple to add an extra element to the
> struct swit that included the value to return, so these things could be
> automatically indexed via enum (or whatever).  In other words, the above
> code would convert to:
> 
> enum { AUDSW, NAUDSW, CHGSW, NCHGSW, };
> static struct swit switches[] = {
>    { "audit audit-file", 0, AUDSW },
>    { "noaudit", 0, NAUDSW},
>    { "changecur", 0, CHGSW },
>    { "nochangecur", 0, NCHGSW },
> 
> And the rest of the code would work normally.  Thoughts?

FWIW, the Plan 9 idiom for this is something like:

enum {
  AUDSW = 0,
  NAUDSW,
  CHGSW
  NCHGSW,
  ...
}

typedef struct swit switches[] {
  { "audit audit-file", 0},
  ...
}


The advantage is having symbolic values in the source debugger rather than 
opaque translations from cpp.  I'm all in favour of this. It's a godsend when 
you're tracing code.