https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68395
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Using -std=gnu++17 -fconcepts this compiles OK with GCC 7, 8 and 9. Rejected
with trunk:
bug5.cpp:72:3: warning: access declarations are deprecated in favour of
using-declarations; suggestion: add the 'using' keyword [-Wdeprecated]
72 | detail_tuple::TupleBase<std::index_sequence_for<>,
Values...>::TupleBase;
| ^~~~~~~~~~~~
bug5.cpp:84:42: warning: the address of 'void and_c() [with bool ...<anonymous>
= {}]' will never be NULL [-Waddress]
84 | constexpr bool are_equal_length_tuples = and_c<>;
| ^~~~~~~
bug5.cpp:96:11: error: 'cpt_MappableElement' does not constrain a type
96 | and_c<cpt_MappableElement<Indexes>()...>;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
bug5.cpp:86:14: note: concept defined here
86 | concept bool cpt_MappableElement() {
| ^~~~~~~~~~~~~~~~~~~
bug5.cpp:156:1: warning: ISO C++ forbids declaration of 'main' with no type
[-Wreturn-type]
156 | main() {
| ^~~~
bug5.cpp: In instantiation of 'constexpr const bool
htl::detail_concept::mappable_elements<std::F<int, 1>, int>':
bug5.cpp:102:9: required from 'constexpr const bool
htl::detail_concept::mappable_impl<int, const
htl::Tuple<htl::integral_constant<long int, 2>, htl::integral_constant<long
int, 7> >, const htl::Tuple<htl::integral_constant<long int, 3>, long int> >'
bug5.cpp:108:26: required from here
bug5.cpp:94:16: warning: the address of 'void and_c() [with bool ...<anonymous>
= {false}]' will never be NULL [-Waddress]
94 | constexpr bool mappable_elements<std::index_sequence<Indexes...>,
Functor,
|
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
95 | TupleForwards...> =
| ~~~~~~~~~~~~~~~~~
bug5.cpp: In instantiation of 'constexpr const bool
htl::detail_concept::mappable_predicate_impl<int, const
htl::Tuple<htl::integral_constant<long int, 2>, htl::integral_constant<long
int, 7> >, const htl::Tuple<htl::integral_constant<long int, 3>, long int> >':
bug5.cpp:124:26: required from here
bug5.cpp:118:40: warning: the address of 'bool
htl::detail_concept::cpt_MappablePredicateImpl() [with <template-parameter-1-1>
= int]' will never be NULL [-Waddress]
118 | TupleForwards...>() constexpr bool
mappable_predicate_impl<Predicate,
|
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
119 |
TupleForwards...> =
|
~~~~~~~~~~~~~~~~~
