https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87017
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. it only works with clang and ICC because you're using them with an older
version of libstdc++, which didn't enforce this requirement. Saying "it
compiles with three compilers all using the same standard library" is only one
data point.
If you use clang's own libc++ you get a similar error:
In file included from /opt/wandbox/clang-head/include/c++/v1/regex:770:
/opt/wandbox/clang-head/include/c++/v1/vector:486:5: error: static_assert
failed due to requirement 'is_same<typename allocator_type::value_type,
value_type>::value' "Allocator::value_type must be same type as value_type"
static_assert((is_same<typename allocator_type::value_type,
value_type>::value),
^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/clang-head/include/c++/v1/regex:5228:23: note: in instantiation of
template class
'std::__1::vector<std::__1::sub_match<std::__1::__wrap_iter<const char *> >,
FaF::Allocator<std::__1::__wrap_iter<const char *> > >' requested here
__container_type __matches_;
^
prog.cc:33:15: note: in instantiation of template class
'std::__1::match_results<std::__1::__wrap_iter<const char *>,
FaF::Allocator<std::__1::__wrap_iter<const char *> > >' requested here
FaF::smatch results {};
^
That's because the code is not valid according to the standard.
