capture parameter pack as a tuple to work around gcc4.8

[bkietz]

fixes #69

repro: https://wandbox.org/permlink/po7niLIoJ9HgJ74p
fixed: https://wandbox.org/permlink/RTg6mAArF13XyuRU

There are more sophisticated/general implementations of make_index_sequence/apply if desired

[jimhester]

Great, thanks!

Do you think we should use this new implementation in all cases, or only when older gcc versions are used?

[bkietz]

There's no performance overhead (runtime or compile time) so I'd say: it's simpler to just leave it this way until gcc 4.8 can be dropped

[jimhester]

I think we may have to do the same thing with the parameter packs in cpp11::stop and cpp11::warning as well? I get the following errors when trying to compile tidyr with this PR

g++ -std=gnu++11 -I"/opt/R/4.0.2/lib/R/include" -DNDEBUG  -I'/opt/R/4.0.2/lib/R/library/cpp11/include' -I/usr/local/include   -fpic  -g -O2  -c cpp11.cpp -o cpp11.o
In file included from /opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/as.hpp:8:0,
                 from /opt/R/4.0.2/lib/R/library/cpp11/include/cpp11.hpp:5,
                 from /opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/declarations.hpp:8,
                 from cpp11.cpp:4:
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp: In lambda function:
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:245:38: error: parameter packs not expanded with ‘...’:
   unwind_protect([&] { Rf_error(fmt, args...); });
                                      ^
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:245:38: note:         ‘args’
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:245:42: error: expansion pattern ‘args’ contains no argument packs
   unwind_protect([&] { Rf_error(fmt, args...); });
                                          ^
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp: In lambda function:
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:253:46: error: parameter packs not expanded with ‘...’:
   unwind_protect([&] { Rf_error(fmt.c_str(), args...); });
                                              ^
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:253:46: note:         ‘args’
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:253:50: error: expansion pattern ‘args’ contains no argument packs
   unwind_protect([&] { Rf_error(fmt.c_str(), args...); });
                                                  ^
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp: In instantiation of ‘struct cpp11::stop(const char*, Args ...) [with Args = {}]::__lambda3’:
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:245:49:   required from ‘void cpp11::stop(const char*, Args ...) [with Args = {}]’
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/as.hpp:98:39:   required from ‘cpp11::is_logical<T> cpp11::as_cpp(SEXP) [with T = bool; cpp11::is_logical<T> = bool; SEXP = SEXPREC*]’
cpp11.cpp:24:452:   required from here
/opt/R/4.0.2/lib/R/library/cpp11/include/cpp11/protect.hpp:245:38: error: using invalid field ‘cpp11::stop(const char*, Args ...)::__lambda3::__args’
   unwind_protect([&] { Rf_error(fmt, args...); });
                                      ^

But this does fix the errors with safe, so I think it is a good workaround.

[bkietz]

actually, those errors are all from stop(). I think we can just use safe in stop() as we do in warning()

[jimhester]

Cool, can confirm these changes fix compilation on 4.8.5, thanks @bkietz for working through this! People will definitely be happy they can use cpp11 on older gcc versions.