From: David Alan Black <dblack@...>
Date: 2001-09-09T05:22:59+09:00
Subject: [ruby-talk:21014] Re: length of Ruby array from C?

Hello --

On Sun, 9 Sep 2001, Neil Conway wrote:

> Hi all,
>
> 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:

  [...]
  For example, `RSTRING(size)->len' is the way to get the size of the
  Ruby String object.  The allocated region can be accessed by
  `RSTRING(str)->ptr'.  For arrays, `RARRAY(ary)->len' and
  `RARRAY(ary)->ptr' respectively.


> 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.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav