index

/*
 *  call-seq:
 *     hsh.index(value)    => key
 *
 *  Returns the key for a given value. If not found, returns <code>nil</code>.
 *
 *     h = { "a" => 100, "b" => 200 }
 *     h.index(200)   #=> "b"
 *     h.index(999)   #=> nil
 *
 */

static VALUE
rb_hash_index(hash, value)
    VALUE hash, value;
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, index_i, (st_data_t)args);

    return args[1];
}