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compile error on requires to_view #220
Description
I want to check if rfl::to_view() can be applied to a variable of type T, but the following code fails to compile:
template<class T>
void FailedToCompile(T const& t) {
if constexpr (requires { rfl::to_view(t); }) {
}
}
int main() {
std::string s = "hello";
FailedToCompile(s);
}As a workaround, I have to use std::is_aggregate_v<T> for the check instead.
Would it be possible to add a concept constraint requiring rfl::to_view to only be applicable when T satisfies std::is_aggregate_v<T>? That way, the if constexpr (requires { rfl::to_view(t); }) condition would work as expected.
Activity
liuzicheng1987 commentedon Oct 16, 2024
Hi @zhuoqiang , what error message do you get when you do this?
zhuoqiang commentedon Oct 16, 2024
@liuzicheng1987
In file included from /rfl/internal/get_ith_field_from_fake_object.hpp:13, from /rfl/internal/get_field_names.hpp:12, from /rfl/field_names_t.hpp:7, from /rfl/internal/to_ptr_named_tuple.hpp:9, from /rfl/to_view.hpp:8, from main.cpp:1: /rfl/internal/num_fields.hpp: In instantiation of 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_max_args_in_agg() [with long unsigned int n = 33; T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]': /rfl/internal/num_fields.hpp:107:42: required from 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_fields() [with T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]' 107 | return count_max_args_in_agg<n + 1>(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/num_fields.hpp:208:70: required from 'constexpr const std::size_t rfl::internal::num_fields<std::__cxx11::basic_string<char> >' 208 | constexpr std::size_t num_fields = CountFieldsHelper<T>::count_fields(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/bind_to_tuple.hpp:551:28: required from 'auto rfl::internal::tuple_view(T&) [with T = std::__cxx11::basic_string<char>]' 551 | return tuple_view_helper<num_fields<T>>::tuple_view(t); | ^~~~~~~~~~~~ /rfl/internal/bind_to_tuple.hpp:556:25: required from 'auto rfl::internal::bind_to_tuple(T&, const F&) [with T = std::__cxx11::basic_string<char>; F = to_ptr_tuple<std::__cxx11::basic_string<char> >(std::__cxx11::basic_string<char>&)::<lambda(auto:362*)>]' 556 | auto view = tuple_view(_t); | ~~~~~~~~~~^~~~ /rfl/internal/to_ptr_tuple.hpp:18:25: required from 'auto rfl::internal::to_ptr_tuple(T&) [with T = std::__cxx11::basic_string<char>]' 18 | return bind_to_tuple(_t, [](auto* _ptr) { return _ptr; }); | ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /rfl/internal/ptr_tuple_t.hpp:13:42: required by substitution of 'template<class T> using rfl::internal::ptr_tuple_t = decltype (rfl::internal::to_ptr_tuple(declval<T&>())) [with T = std::__cxx11::basic_string<char>]' 13 | using ptr_tuple_t = decltype(to_ptr_tuple(std::declval<T&>())); | ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ /rfl/internal/has_fields.hpp:61:11: required from 'constexpr bool rfl::internal::has_fields() [with T = std::__cxx11::basic_string<char>]' 61 | using TupleType = ptr_tuple_t<T>; | ^~~~~~~~~ /rfl/internal/to_ptr_named_tuple.hpp:61:51: required from 'auto rfl::internal::to_ptr_named_tuple(T&&) [with T = const std::__cxx11::basic_string<char>&]' 61 | if constexpr (has_fields<std::remove_cvref_t<T>>()) { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/to_view.hpp:14:38: required from 'auto rfl::to_view(T&) [with T = const std::__cxx11::basic_string<char>]' 14 | return internal::to_ptr_named_tuple(_t); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~ main.cpp:8:40: required from 'void FailedToCompile(const T&) [with T = std::__cxx11::basic_string<char>]' 8 | if constexpr (requires { rfl::to_view(t); }) { | ~~~~~~~~~~~~^~~ main.cpp:14:18: required from here 14 | FailedToCompile(s); | ~~~~~~~~~~~~~~~^~~ /rfl/internal/num_fields.hpp:184:63: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<1>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<2>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<3>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<4>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<5>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<6>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<7>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<8>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<9>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<10>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<11>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<12>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<13>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<14>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<15>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<16>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<17>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<18>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<19>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<20>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<21>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<22>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<23>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<24>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<25>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<26>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<27>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<28>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<29>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<30>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<31>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<32>()' /rfl/internal/num_fields.hpp:103:21: error: static assertion failed 103 | static_assert(n <= static_cast<std::size_t>(sizeof(T))); | ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /rfl/internal/num_fields.hpp:103:21: note: the comparison reduces to '(33 <= 32)' /rfl/internal/num_fields.hpp: In instantiation of 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_max_args_in_agg() [with long unsigned int n = 34; T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]': /rfl/internal/num_fields.hpp:107:42: required from 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_fields() [with T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]' 107 | return count_max_args_in_agg<n + 1>(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/num_fields.hpp:208:70: required from 'constexpr const std::size_t rfl::internal::num_fields<std::__cxx11::basic_string<char> >' 208 | constexpr std::size_t num_fields = CountFieldsHelper<T>::count_fields(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/bind_to_tuple.hpp:551:28: required from 'auto rfl::internal::tuple_view(T&) [with T = std::__cxx11::basic_string<char>]' 551 | return tuple_view_helper<num_fields<T>>::tuple_view(t); | ^~~~~~~~~~~~ /rfl/internal/bind_to_tuple.hpp:556:25: required from 'auto rfl::internal::bind_to_tuple(T&, const F&) [with T = std::__cxx11::basic_string<char>; F = to_ptr_tuple<std::__cxx11::basic_string<char> >(std::__cxx11::basic_string<char>&)::<lambda(auto:362*)>]' 556 | auto view = tuple_view(_t); | ~~~~~~~~~~^~~~ /rfl/internal/to_ptr_tuple.hpp:18:25: required from 'auto rfl::internal::to_ptr_tuple(T&) [with T = std::__cxx11::basic_string<char>]' 18 | return bind_to_tuple(_t, [](auto* _ptr) { return _ptr; }); | ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /rfl/internal/ptr_tuple_t.hpp:13:42: required by substitution of 'template<class T> using rfl::internal::ptr_tuple_t = decltype (rfl::internal::to_ptr_tuple(declval<T&>())) [with T = std::__cxx11::basic_string<char>]' 13 | using ptr_tuple_t = decltype(to_ptr_tuple(std::declval<T&>())); | ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ /rfl/internal/has_fields.hpp:61:11: required from 'constexpr bool rfl::internal::has_fields() [with T = std::__cxx11::basic_string<char>]' 61 | using TupleType = ptr_tuple_t<T>; | ^~~~~~~~~ /rfl/internal/to_ptr_named_tuple.hpp:61:51: required from 'auto rfl::internal::to_ptr_named_tuple(T&&) [with T = const std::__cxx11::basic_string<char>&]' 61 | if constexpr (has_fields<std::remove_cvref_t<T>>()) { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/to_view.hpp:14:38: required from 'auto rfl::to_view(T&) [with T = const std::__cxx11::basic_string<char>]' 14 | return internal::to_ptr_named_tuple(_t); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~ main.cpp:8:40: required from 'void FailedToCompile(const T&) [with T = std::__cxx11::basic_string<char>]' 8 | if constexpr (requires { rfl::to_view(t); }) { | ~~~~~~~~~~~~^~~ main.cpp:14:18: required from here 14 | FailedToCompile(s); | ~~~~~~~~~~~~~~~^~~ /rfl/internal/num_fields.hpp:184:63: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<1>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<2>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<3>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<4>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<5>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<6>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<7>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<8>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<9>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<10>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<11>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<12>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<13>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<14>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<15>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<16>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<17>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<18>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<19>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<20>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<21>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<22>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<23>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<24>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<25>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<26>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<27>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<28>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<29>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<30>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<31>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<32>()' /rfl/internal/num_fields.hpp:107:42: in 'constexpr' expansion of 'rfl::internal::CountFieldsHelper<std::__cxx11::basic_string<char> >::count_max_args_in_agg<33>()' /rfl/internal/num_fields.hpp:103:21: error: static assertion failed 103 | static_assert(n <= static_cast<std::size_t>(sizeof(T))); | ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /rfl/internal/num_fields.hpp:103:21: note: the comparison reduces to '(34 <= 32)' /rfl/internal/num_fields.hpp: In instantiation of 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_max_args_in_agg() [with long unsigned int n = 35; T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]': /rfl/internal/num_fields.hpp:107:42: required from 'static consteval std::size_t rfl::internal::CountFieldsHelper<T>::count_fields() [with T = std::__cxx11::basic_string<char>; std::size_t = long unsigned int]' 107 | return count_max_args_in_agg<n + 1>(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/num_fields.hpp:208:70: required from 'constexpr const std::size_t rfl::internal::num_fields<std::__cxx11::basic_string<char> >' 208 | constexpr std::size_t num_fields = CountFieldsHelper<T>::count_fields(); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/internal/bind_to_tuple.hpp:551:28: required from 'auto rfl::internal::tuple_view(T&) [with T = std::__cxx11::basic_string<char>]' 551 | return tuple_view_helper<num_fields<T>>::tuple_view(t); | ^~~~~~~~~~~~ /rfl/internal/bind_to_tuple.hpp:556:25: required from 'auto rfl::internal::bind_to_tuple(T&, const F&) [with T = std::__cxx11::basic_string<char>; F = to_ptr_tuple<std::__cxx11::basic_string<char> >(std::__cxx11::basic_string<char>&)::<lambda(auto:362*)>]' 556 | auto view = tuple_view(_t); | ~~~~~~~~~~^~~~ /rfl/internal/to_ptr_tuple.hpp:18:25: required from 'auto rfl::internal::to_ptr_tuple(T&) [with T = std::__cxx11::basic_string<char>]' 18 | return bind_to_tuple(_t, [](auto* _ptr) { return _ptr; }); | ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ /rfl/internal/ptr_tuple_t.hpp:13:42: required by substitution of 'template<class T> using rfl::internal::ptr_tuple_t = decltype (rfl::internal::to_ptr_tuple(declval<T&>())) [with T = std::__cxx11::basic_string<char>]' 13 | using ptr_tuple_t = decltype(to_ptr_tuple(std::declval<T&>())); | ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~ /rfl/internal/has_fields.hpp:61:11: required from 'constexpr bool rfl::internal::has_fields() [with T = std::__cxx11::basic_string<char>]' 61 | using TupleType = ptr_tuple_t<T>; | ^~~~~~~~~ /rfl/internal/to_ptr_named_tuple.hpp:61:51: required from 'auto rfl::internal::to_ptr_named_tuple(T&&) [with T = const std::__cxx11::basic_string<char>&]' 61 | if constexpr (has_fields<std::remove_cvref_t<T>>()) { | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ /rfl/to_view.hpp:14:38: required from 'auto rfl::to_view(T&) [with T = const std::__cxx11::basic_string<char>]' 14 | return internal::to_ptr_named_tuple(_t); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~ main.cpp:8:40: required from 'void FailedToCompile(const T&) [with T = std::__cxx11::basic_string<char>]' 8 | if constexpr (requires { rfl::to_view(t); }) { | ~~~~~~~~~~~~^~~ main.cpp:14:18: required from here 14 | FailedToCompile(s); | ~~~~~~~~~~~~~~~^~~liuzicheng1987 commentedon Oct 16, 2024
Interesting...this apparently happens when you try to insert a string.
I think this could be resolved with a well-placed constexpr if.
I will take a look.
zhuoqiang commentedon Oct 16, 2024
no need to do actual actions, the following constexpr check is enough to reproduce the compile error: