Kojoley
commented
3 years ago The original char_('+') >> term has an attribute of tuple<char, ast::program> and it could be converted to ast::operation (struct operation { char operator_; operand operand_; };), the latter char_('+') has an attribute of char and there is no conversion from it to ast::operation. Qi is ok with that because of a https://svn.boost.org/trac10/ticket/8013 bug.
/usr/include/boost/fusion/algorithm/auxiliary/move.hpp:50:23: error: cannot convert ‘std::remove_referenceclient::ast::operand&::type’ {aka ‘client::ast::operand’} to ‘char’ in assignment
50 | *dest = std::move(*src);I do not know why it is reversed in your error message, for me Clang says:
boost/spirit/home/x3/support/traits/move_to.hpp:196:9: error: no matching function for call to 'move_to'
detail::move_to(src, dest, typename attribute_category<Dest>::type());
^~~~~~~~~~~~~~~
boost/spirit/home/x3/char/char_parser.hpp:31:29: note: in instantiation of function template
specialization 'boost::spirit::x3::traits::move_to<const char &, client::ast::operation>' requested here
x3::traits::move_to(*first, attr);
^
...If there were a static assert message, let's imagine saying Cannot convert an attribute of a parser to an actual attribute, would you figure out the issue in your parser yourself?
vehlwn
Boost-1.75.0. Consider two equivalent calc4 examples: in spirit::qi: https://github.com/boostorg/spirit/blob/e0625d190bef75ce9be96b1963f153c3c9e65ada/example/qi/compiler_tutorial/calc4.cpp#L202 in spirit::x3: https://github.com/boostorg/spirit/blob/e0625d190bef75ce9be96b1963f153c3c9e65ada/example/x3/calc/calc4.cpp#L187
When I change in qi version:
expression = term >> *((char_('+') >> term) | (char_('-') >> term));toexpression = term >> *((char_('+') | char_('-')) >> term);it works.But when I do the same replacement in x3 version:
auto const expression_def = term >> *((char_('+') >> term) | (char_('-') >> term));toauto const expression_def = term >> *((char_('+') | char_('-')) >> term);it fails to compile with the following errors:/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:196:24: error: no matching function for call to ‘move_to(const char&, client::ast::operation&, boost::mpl::identity::type)’
196 | detail::move_to(src, dest, typename attribute_category::type());
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:56:9: note: candidate: ‘template<class Source, class Dest> void boost::spirit::x3::traits::detail::move_to(Source&, Dest&, boost::spirit::x3::traits::unused_attribute)’
56 | move_to(Source&, Dest&, unused_attribute) {}
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:56:9: note: template argument deduction/substitution failed:
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:196:71: note: cannot convert ‘boost::mpl::identity::type()’ (type ‘boost::mpl::identity::type’ {aka ‘boost::spirit::x3::traits::tuple_attribute’}) to type ‘boost::spirit::x3::traits::unused_attribute’
196 | detail::move_to(src, dest, typename attribute_category::type());
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:74:9: note: candidate: ‘template<class Source, class Dest> void boost::spirit::x3::traits::detail::move_to(Source&, Dest&, boost::spirit::x3::traits::plain_attribute)’
74 | move_to(Source& src, Dest& dest, plain_attribute)
...
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp:97:9: error: no type named ‘type’ in ‘struct boost::enableif<boost::mpl::and<boost::spirit::x3::traits::is_same_sizesequence<client::ast::operation, const char>, boost::mpl::not<boost::spirit::x3::traits::is_size_onesequence >, mpl ::bool, mpl ::bool, mpl ::bool_ >, void>’
/usr/include/boost/spirit/home/x3/support/traits/move_to.hpp: In instantiation of ‘void boost::spirit::x3::traits::move_to(Source&&, Dest&) [with Source = const char&; Dest = client::ast::operation]’:
/usr/include/boost/spirit/home/x3/char/char_parser.hpp:31:36: required from ‘bool boost::spirit::x3::char_parser::parse(Iterator&, const Iterator&, const Context&, boost::spirit::x3::unused_type, Attribute&) const [with Iterator = gnu_cxx::__normal_iterator<const char*, std::cxx11::basic_string >; Context = boost::spirit::x3::context<boost::spirit::x3::skipper_tag, const boost::spirit::x3::char_class<boost::spirit::char_encoding::ascii, boost::spirit::x3::space_tag>, boost::spirit::x3::unused_type>; Attribute = client::ast::operation; Derived = boost::spirit::x3::literal_char<boost::spirit::char_encoding::standard, char>]’
...
/usr/include/boost/fusion/algorithm/auxiliary/move.hpp:50:23: error: cannot convert ‘std::remove_reference<client::ast::operand&>::type’ {aka ‘client::ast::operand’} to ‘char’ in assignment
50 | dest = std::move(src);
I can attach a full compiler transcript if it's needed. Looks like a regression in x3 version.