inspect

static VALUE
rb_io_inspect(VALUE obj)
{
    rb_io_t *fptr;
    const char *cname;
    char fd_desc[4+sizeof(int)*3];
    const char *path;
    const char *st = "";

    fptr = RFILE(rb_io_taint_check(obj))->fptr;
    if (!fptr) return rb_any_to_s(obj);
    cname = rb_obj_classname(obj);
    if (NIL_P(fptr->pathv)) {
        if (fptr->fd < 0) {
            path = "";
            st = "(closed)";
        }
        else {
            snprintf(fd_desc, sizeof(fd_desc), "fd %d", fptr->fd);
            path = fd_desc;
        }
    }
    else {
        path = RSTRING_PTR(fptr->pathv);
        if (fptr->fd < 0) {
            st = " (closed)";
        }
    }
    return rb_sprintf("#<%s:%s%s>", cname, path, st);
}