struct.c:390
static VALUE
rb_struct_inspect(s)
    VALUE s;
{
    if (rb_inspecting_p(s)) {
	char *cname = rb_class2name(rb_obj_class(s));
	VALUE str = rb_str_new(0, strlen(cname) + 15);

	sprintf(RSTRING(str)->ptr, "#<struct %s:...>", cname);
	RSTRING(str)->len = strlen(RSTRING(str)->ptr);
	return str;
    }
    return rb_protect_inspect(inspect_struct, s, 0);
}
