build failure with gcc 7 and 8

[revive]

Failure appears when building the test-range-util.cc with g++ version 7 or 8. The compiler reports that sorry, unimplemented: mangling decltype in the auto zip(Range&&... ranges) function.
No problem found when building with g++ version 5, 6 and clang.

[XeCycle]

I'm not sure what's happening but this patch can workaround that. I think I need some more time with this, not sure if I could land this patch as-is.

diff --git a/include/bs3/utils/range-util.hh b/include/bs3/utils/range-util.hh
index 0a75018..16e804e 100644
--- a/include/bs3/utils/range-util.hh
+++ b/include/bs3/utils/range-util.hh
@@ -154,9 +154,14 @@ struct zip_iterator_impl<std_bp::index_sequence<i...>, Iterator...> {
 
 };
 
+template <class... T>
+struct sizeof_pack {
+  constexpr static size_t value = sizeof...(T);
+};
+
 template <class... Iterator>
 using zip_iterator = zip_iterator_impl<
-  std_bp::make_index_sequence<sizeof...(Iterator)>,
+  std_bp::make_index_sequence<sizeof_pack<Iterator...>::value>,
   Iterator...
 >;
 

[revive]

Thanks. The porting tutorials of gcc 7 and gcc 8 don't mention anything about this update. Btw, I suggest to abandon the support of c++11, but using c++14 by default.

[XeCycle]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87786
I think it's a GCC bug. If the GCC devs agree I'll land this as a workaround.

[revive]

The status of the bug report is still unconfirmed. Seems that no one has worked on it.