From: Christer Sandberg <sillen@...>
Date: 2006-09-21T17:46:46+09:00
Subject: Re: Creating a reference to a ruby variable in a C extension

David Balmain wrote:
> On 9/21/06, Christer Sandberg <chrsan@gmail.com> wrote:
>> Vincent Fourmond wrote:
>> > Hello !
>> >
>> >> Then later on I wan't to use it like this:
>> >>
>> >> void call(void)
>> >> {
>> >>   rb_funcall(ref, rb_intern("some_method"), 0, 0);
>> >> }
>> >
>> >   How comes this function has no parameters ? Is it being called from
>> > ruby, or only from C code ?
>> >
>>
>> Thank you for the reply, I'll try to clear things up a bit and explain
>> what I want to do.
>>
>> The function is just an example for the sake of making my question a bit
>> clearer. The real functions I am using has parameters. Those functions
>> such as the one above will only be called from C code.
>>
>> >
>> >   I tend to think that using global variables is not a really good 
>> idea.
>> >  We need a bit more context about what you want to do. Is it a class ?
>> > Will it have several instances ?
>> >
>> >   In the latter case, have a look at rb_iv_get and rb_iv_set to get/set
>> > instance variables of a class instance, something like
>> >
>> >   rb_iv_set(self, rb_intern("@variable"), arg); /* in init(...) */
>> >
>> >   and
>> >
>> >
>> > 
>> rb_funcall(rb_iv_get(self,rb_intern("@variable")),rb_intern("some_method"), 
>>
>> > 0, 0); /* in call */
>> >
>>
>> Yes, I'm writing a tiny Ruby class in C that wraps and uses a bison/flex
>> generated parser. The saved variable reference will be used for making
>> calls on the ruby instance. When those calls are made self is long gone
>> out of scope sice it's the parser who triggers the method call. The C
>> Ruby class just acts as a proxy or adapter between the parser and the
>> Ruby object.
> 
> Hi Christer,
> 
> Instead of saving it as a global variable, you could save it as a
> class variable. See rb_cvar_[gs]et (defined in variable.c). Just an
> idea.
> 
> Cheers,
> Dave
> 

Hi Dave!

That would work if the passed in object should be shared among all 
instances of my class, but that's not the case since it's a callback 
object that's supplied for a particular instance of my class.

Correct me if I'm wrong but the variable is only global in my C code 
since I haven't made it visible to the Ruby environment with a 
rb_gv_set(const char *name, VALUE value)?

Thanx
Christer