Forum: Ruby rb_hash_aref and symbol keys

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Andre N. (Guest)
on 2006-04-07 18:30
(Received via mailing list)
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 :( */

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
ts (Guest)
on 2006-04-07 18:42
(Received via mailing list)
>>>>> "A" == Andre N. <removed_email_address@domain.invalid> writes:

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

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


Guy Decoux
Andre N. (Guest)
on 2006-04-07 18:45
(Received via mailing list)
On Fri, 2006-04-07 at 23:42 +0900, ts wrote:
>    foo = rb_hash_aref(myhash, ID2SYM(rb_intern("foo")));

Thanks a lot!

Andre
Yukihiro M. (Guest)
on 2006-04-07 19:04
(Received via mailing list)
Hi,

In message "Re: rb_hash_aref and symbol keys"
    on Fri, 7 Apr 2006 23:28:17 +0900, Andre N.
<removed_email_address@domain.invalid> writes:

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

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.
Andre N. (Guest)
on 2006-04-07 20:17
(Received via mailing list)
On Sat, 2006-04-08 at 00:02 +0900, Yukihiro M. 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.

Andre
Yukihiro M. (Guest)
on 2006-04-07 21:09
(Received via mailing list)
In message "Re: rb_hash_aref and symbol keys"
    on Sat, 8 Apr 2006 01:16:48 +0900, Andre N.
<removed_email_address@domain.invalid> writes:
|
|On Sat, 2006-04-08 at 00:02 +0900, Yukihiro M. 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.

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)
Andre N. (Guest)
on 2006-04-07 21:09
(Received via mailing list)
On Sat, 2006-04-08 at 02:07 +0900, Yukihiro M. wrote:
> I will update the following section in README.EXT:

Perfect! Thanks again :)

Andre
Yukihiro M. (Guest)
on 2006-04-07 21:18
(Received via mailing list)
Hi,

In message "Re: rb_hash_aref and symbol keys"
    on Sat, 8 Apr 2006 02:09:03 +0900, Andre N.
<removed_email_address@domain.invalid> writes:

|On Sat, 2006-04-08 at 02:07 +0900, Yukihiro M. wrote:
|> I will update the following section in README.EXT:
|
|Perfect! Thanks again :)

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.
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