to_s

/*
 *  call-seq:
 *     rxp.to_s   => str
 *  
 *  Returns a string containing the regular expression and its options (using the
 *  <code>(?xxx:yyy)</code> notation. This string can be fed back in to
 *  <code>Regexp::new</code> to a regular expression with the same semantics as
 *  the original. (However, <code>Regexp#==</code> may not return true when
 *  comparing the two, as the source of the regular expression itself may
 *  differ, as the example shows).  <code>Regexp#inspect</code> produces a
 *  generally more readable version of <i>rxp</i>.
 *     
 *     r1 = /ab+c/ix         #=> /ab+c/ix
 *     s1 = r1.to_s          #=> "(?ix-m:ab+c)"
 *     r2 = Regexp.new(s1)   #=> /(?ix-m:ab+c)/
 *     r1 == r2              #=> false
 *     r1.source             #=> "ab+c"
 *     r2.source             #=> "(?ix-m:ab+c)"
 */

static VALUE
rb_reg_to_s(re)
    VALUE re;
{
    int options;
    const int embeddable = RE_OPTION_MULTILINE|RE_OPTION_IGNORECASE|RE_OPTION_EXTENDED;
    long len;
    const char* ptr;
    VALUE str = rb_str_buf_new2("(?");

    rb_reg_check(re);

    options = RREGEXP(re)->ptr->options;
    ptr = RREGEXP(re)->str;
    len = RREGEXP(re)->len;
  again:
    if (len >= 4 && ptr[0] == '(' && ptr[1] == '?') {
        int err = 1;
        ptr += 2;
        if ((len -= 2) > 0) {
            do {
                if (*ptr == 'm') {
                    options |= RE_OPTION_MULTILINE;
                }
                else if (*ptr == 'i') {
                    options |= RE_OPTION_IGNORECASE;
                }
                else if (*ptr == 'x') {
                    options |= RE_OPTION_EXTENDED;
                }
                else break;
                ++ptr;
            } while (--len > 0);
        }
        if (len > 1 && *ptr == '-') {
            ++ptr;
            --len;
            do {
                if (*ptr == 'm') {
                    options &= ~RE_OPTION_MULTILINE;
                }
                else if (*ptr == 'i') {
                    options &= ~RE_OPTION_IGNORECASE;
                }
                else if (*ptr == 'x') {
                    options &= ~RE_OPTION_EXTENDED;
                }
                else break;
                ++ptr;
            } while (--len > 0);
        }
        if (*ptr == ')') {
            --len;
            ++ptr;
            goto again;
        }
        if (*ptr == ':' && ptr[len-1] == ')') {
            Regexp *rp;
            rb_kcode_set_option(re);
            rp = ALLOC(Regexp);
            MEMZERO((char *)rp, Regexp, 1);
            err = re_compile_pattern(++ptr, len -= 2, rp) != 0;
            rb_kcode_reset_option();
            re_free_pattern(rp);
        }
        if (err) {
            options = RREGEXP(re)->ptr->options;
            ptr = RREGEXP(re)->str;
            len = RREGEXP(re)->len;
        }
    }

    if (options & RE_OPTION_MULTILINE) rb_str_buf_cat2(str, "m");
    if (options & RE_OPTION_IGNORECASE) rb_str_buf_cat2(str, "i");
    if (options & RE_OPTION_EXTENDED) rb_str_buf_cat2(str, "x");

    if ((options & embeddable) != embeddable) {
        rb_str_buf_cat2(str, "-");
        if (!(options & RE_OPTION_MULTILINE)) rb_str_buf_cat2(str, "m");
        if (!(options & RE_OPTION_IGNORECASE)) rb_str_buf_cat2(str, "i");
        if (!(options & RE_OPTION_EXTENDED)) rb_str_buf_cat2(str, "x");
    }

    rb_str_buf_cat2(str, ":");
    rb_reg_expr_str(str, ptr, len);
    rb_str_buf_cat2(str, ")");

    OBJ_INFECT(str, re);
    return str;
}