Method precall

include/pybind11/attr.h:690–695

                        (process_attribute<typename std::decay<Args>::type>::init(args, r), 0)...};
    }
    static void precall(function_call &call) {
        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call);
        using expander = int[];
        (void) expander{0,
                        (process_attribute<typename std::decay<Args>::type>::precall(call), 0)...};
    }
    static void postcall(function_call &call, handle fn_ret) {
        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(call, fn_ret);
        PYBIND11_WORKAROUND_INCORRECT_GCC_UNUSED_BUT_SET_PARAMETER(fn_ret);