From: nobu.nokada@...
Date: 2003-11-28T14:06:23+09:00
Subject: Re: rb_hash_aref question: symbols vs strings

Hi,

At Fri, 28 Nov 2003 11:32:08 +0900,
Daniel Berger wrote:
> If the key "bar" is a string, that works fine.  However, that returns
> nil (not a symbol) if "bar" is a symbol.  I know I can do rb_iterate
> and I can detect if hash keys are symbols, but I don't know how to
> permanately change the key back to a string, i.e. it appears to pass a
> copy of the hash, rather than a reference.

Do you use Hash#each_pair or similar?  They just ignore
returned values from yielded blocks.

> // Iterate over hash.  Assume that rb_sym2str() works properly.

No such function.  Instead, you can use rb_to_id() vice versa.

===File foo.c===============================================
#include <ruby.h>

enum {
    Foo_test_bar,
    Foo_test_baz,
    Foo_test_MAX
};

typedef VALUE Foo_test_options[Foo_test_MAX];

static ID id_Foo_test[Foo_test_MAX];

static VALUE
parse_hash(VALUE array, Foo_test_options opt)
{
    ID key = rb_to_id(RARRAY(array)->ptr[0]);
    VALUE val = RARRAY(array)->ptr[1];
    int i;

    for (i = 0; i < Foo_test_MAX; ++i) {
	if (key == id_Foo_test[i]) {
	    opt[i] = val;
	    return Qnil;
	}
    }
    rb_raise(rb_eArgError, "unknown option - %s", rb_id2name(key));
    return Qnil;		/* not reached */
}

static VALUE
foo_s_test(VALUE self, VALUE args)
{
    Foo_test_options opt;
    VALUE a[3];
    int i;

    Check_Type(args, T_HASH);
    for (i = 0; i < Foo_test_MAX; ++i) {
	opt[i] = Qundef;
    }
    rb_iterate(rb_each, args, parse_hash, (VALUE)opt);
    a[0] = rb_str_new2("%p=%p\n");
    for (i = 0; i < Foo_test_MAX; ++i) {
	if (opt[i] != Qundef) {
	    a[1] = ID2SYM(id_Foo_test[i]);
	    a[2] = opt[i];
	    rb_io_printf(3, a, rb_stdout);
	}
    }
    return self;
}

void
Init_foo(void)
{
    VALUE foo = rb_define_class("Foo", rb_cObject);
    rb_define_singleton_method(foo, "test", foo_s_test, 1);
    id_Foo_test[Foo_test_bar] = rb_intern("bar");
    id_Foo_test[Foo_test_baz] = rb_intern("baz");
}
============================================================

You can use struct instead of array.

-- 
Nobu Nakada