Rb_hash_aref and symbol keys


#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

“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 :frowning: */

foo = rb_hash_aref(myhash, ID2SYM(rb_intern(“foo”)));

Guy Decoux


#3

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

foo = rb_hash_aref(myhash, ID2SYM(rb_intern(“foo”)));

Thanks a lot!

Andre


#4

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


#5

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 :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.

#6

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)


#7

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

I will update the following section in README.EXT:

Perfect! Thanks again :slight_smile:

Andre


#8

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 :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.