IO#inspect

static VALUE
rb_io_inspect(VALUE obj)
{
    rb_io_t *fptr;
    VALUE result;
    static const char closed[] = " (closed)";

    fptr = RFILE(obj)->fptr;
    if (!fptr) return rb_any_to_s(obj);
    result = rb_str_new_cstr("#<");
    rb_str_append(result, rb_class_name(CLASS_OF(obj)));
    rb_str_cat2(result, ":");
    if (NIL_P(fptr->pathv)) {
        if (fptr->fd < 0) {
            rb_str_cat(result, closed+1, strlen(closed)-1);
        }
        else {
            rb_str_catf(result, "fd %d", fptr->fd);
        }
    }
    else {
        rb_str_append(result, fptr->pathv);
        if (fptr->fd < 0) {
            rb_str_cat(result, closed, strlen(closed));
        }
    }
    return rb_str_cat2(result, ">");
}