From: Neil Conway <nconway@...>
Date: 2001-09-09T05:52:59+09:00
Subject: [ruby-talk:21015] Re: length of Ruby array from C?

On Sat, 2001-09-08 at 16:22, David Alan Black wrote:
> Hello --
> 
> On Sun, 9 Sep 2001, Neil Conway wrote:
> > I've been experimenting with writing some Ruby extensions in C. In order
> > to find the length of a Ruby array, I needed to do this:
> >
> > /* -------- */
> > VALUE ary;
> > int ary_length;
> > /* ... assign a Ruby array to "ary" ... */
> > ary_length = RARRAY(ary)->len;
> > /* -------- */
> >
> > There are 2 problems with this, IMHO:
> >
> > 1) undocumented: I had to look through the source to find this
> 
> It's described in README.EXT, section 1.3:

Woops, sorry about that. I had been using the Pickaxe book, which
doesn't document this. Thanks for the information.

> > 2) clumsy: if this is the only way to get the length, could we perhaps
> > have some syntactic sugar? For instance, a function (or macro)
> > rb_ary_length(VALUE), which returns the length of the specified array as
> > a C integer. Since this is a relatively common operation, I think it
> > would be worthwhile to make it a bit easier for extension writers.
> 
> I think that would be sort of unwieldy, since you'd have to have
> rb_ary_xxxx(VALUE), rb_string_xxxx(VALUE), etc., to replace the
> current way of doing it by accessing C structure members.

I still think this would be a good idea. Of the builtin structs,
'length' only makes sense for RArray and RString. You _could_ add
functions for RRegexp, RBigNum and RStruct, but since these are
relatively rarely used (compared to RArray and RString), there would be
no need to define more than 2 functions -- rb_ary_len(VALUE) and
rb_str_len(VALUE). That's not too unwieldy, IMHO; and I find
"rb_ary_len(ary)" to be more readable than "RARRAY(ary)->len". It also
prevents extension writers from (directly) accessing the fiels of those
structures, which is generally a bad idea (as README.EXT points out).

Cheers,

Neil