inspect

static VALUE
rb_io_inspect(VALUE obj)
{
    rb_io_t *fptr;
    const char *cname;
    const char *st = "";

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