Rb_hash_aref and symbol keys

ruby-talk
1

Hello

I'm just getting starting with ruby C extensions, and I'm having a
problem accessing hash values corresponding to keys which are symbols.
String keys work fine:

/* In ruby: myhash = { 'foo' => 'blah' } */
foo = rb_hash_aref(myhash, rb_str_new2("foo")); /* works */

/* In ruby: myhash = { :foo => 'blah' } */
foo = rb_hash_aref(myhash, rb_intern("foo")); /* returns Qnil :frowning: */

What is the proper way to do that? I found someone with the same problem
in the archives, but I'm afraid I didn't understand Nobu's answer in
ruby-talk:86571 :\

Thanks in advance,
Andre

2

/* In ruby: myhash = { :foo => 'blah' } */
foo = rb_hash_aref(myhash, rb_intern("foo")); /* returns Qnil :frowning: */

   foo = rb_hash_aref(myhash, ID2SYM(rb_intern("foo")));

Guy Decoux

3

Hi,

路路路

In message "Re: rb_hash_aref and symbol keys" on Fri, 7 Apr 2006 23:28:17 +0900, Andre Nathan <andre@digirati.com.br> writes:

/* In ruby: myhash = { :foo => 'blah' } */
foo = rb_hash_aref(myhash, rb_intern("foo")); /* returns Qnil :frowning: */

rb_intern() gives you ID, which is a mere C number. You have to
convert it into a Ruby Symbol Object by using ID2SYM() macro.

              matz.

4

Thanks a lot!

Andre

路路路

On Fri, 2006-04-07 at 23:42 +0900, ts wrote:

   foo = rb_hash_aref(myhash, ID2SYM(rb_intern("foo")));

5

Thank you Matz. Is this documented anywhere? It's not mentioned in
README.EXT.

Andre

路路路

On Sat, 2006-04-08 at 00:02 +0900, Yukihiro Matsumoto wrote:

rb_intern() gives you ID, which is a mere C number. You have to
convert it into a Ruby Symbol Object by using ID2SYM() macro.

6

I will update the following section in README.EXT:

2.2.2 ID or Symbol

You can invoke methods directly, without parsing the string. First I need
to explain about ID. ID is the integer number to represent Ruby's
identifiers such as variable names. The Ruby data type corresponding to ID
is Symbol. It can be accessed from Ruby in the form:

:Identifier

You can get the ID value from a string within C code by using

  rb_intern(const char *name)

You can convert C ID to Ruby Symbol by using

  VALUE ID2SYM(ID id)

and to convert Ruby Symbol to ID, use

  ID SYM2ID(VALUE sym)

路路路

In message "Re: rb_hash_aref and symbol keys" on Sat, 8 Apr 2006 01:16:48 +0900, Andre Nathan <andre@digirati.com.br> writes:

On Sat, 2006-04-08 at 00:02 +0900, Yukihiro Matsumoto wrote:

rb_intern() gives you ID, which is a mere C number. You have to
convert it into a Ruby Symbol Object by using ID2SYM() macro.

Thank you Matz. Is this documented anywhere? It's not mentioned in
README.EXT.

--
              matz.

7

Perfect! Thanks again :slight_smile:

Andre

路路路

On Sat, 2006-04-08 at 02:07 +0900, Yukihiro Matsumoto wrote:

I will update the following section in README.EXT:

8

Hi,

路路路

In message "Re: rb_hash_aref and symbol keys" on Sat, 8 Apr 2006 02:09:03 +0900, Andre Nathan <andre@digirati.com.br> writes:

On Sat, 2006-04-08 at 02:07 +0900, Yukihiro Matsumoto wrote:

I will update the following section in README.EXT:

Perfect! Thanks again :slight_smile:

FYI, Ruby didn't have Symbol objects before. It used to use Fixnums
instead of Symbols. The description in README.EXT reflect the old
situation.

              matz.