Simple Spirit X3 word splitter won't compile, attribute mismatch - c++

Question

I'm trying to use a Spirit X3 parser to process the output from a command-line tool, but have been having issues. I've narrowed them down to a minimal example whose behaviour I don't understand:
#include <string>
#include <vector>
#include <boost/spirit/home/x3.hpp>
int main() {
namespace x3 = boost::spirit::x3;
std::wstring const str = L"bonjour je suis un petit panda";
auto word = x3::lexeme[+x3::alpha];
std::wstring s;
x3::phrase_parse(begin(str), end(str), word, x3::space, s); // OK
std::vector<std::wstring> v;
x3::phrase_parse(begin(str), end(str), *word, x3::space, v); // Compiler error
}
Live demo on Coliru
The error is very hairy, but boils down to not being able to call move_to, which IIUC is a symptom of an attribute type mismatch.
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:180:9: error: no matching function for call to 'move_to'
detail::move_to(std::move(src), dest
^~~~~~~~~~~~~~~
[...]
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:56:9: note: candidate function not viable: no known conversion from 'typename attribute_category<basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > >::type' (aka 'boost::spirit::x3::traits::container_attribute') to 'boost::spirit::x3::traits::unused_attribute' for 3rd argument
move_to(Source&&, Dest&, unused_attribute) {}
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:74:9: note: candidate function not viable: no known conversion from 'typename attribute_category<basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > >::type' (aka 'boost::spirit::x3::traits::container_attribute') to 'boost::spirit::x3::traits::plain_attribute' for 3rd argument
move_to(Source&& src, Dest& dest, plain_attribute)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:97:9: note: candidate function not viable: no known conversion from 'typename attribute_category<basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > >::type' (aka 'boost::spirit::x3::traits::container_attribute') to 'boost::spirit::x3::traits::tuple_attribute' for 3rd argument
move_to(Source&& src, Dest& dest, tuple_attribute)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:106:9: note: candidate function not viable: no known conversion from 'typename attribute_category<basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > >::type' (aka 'boost::spirit::x3::traits::container_attribute') to 'boost::spirit::x3::traits::tuple_attribute' for 3rd argument
move_to(Source&& src, Dest& dest, tuple_attribute)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:150:9: note: candidate function not viable: no known conversion from 'typename attribute_category<basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > >::type' (aka 'boost::spirit::x3::traits::container_attribute') to 'boost::spirit::x3::traits::variant_attribute' for 3rd argument
move_to(Source&& src, Dest& dest, variant_attribute tag)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:85:35: note: candidate template ignored: disabled by 'enable_if' [with Source = const wchar_t, Dest = std::__1::basic_string<wchar_t, std::__1::char_traits<wchar_t>, std::__1::allocator<wchar_t> >]
inline typename enable_if<is_container<Source>>::type
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:113:9: note: candidate function template not viable: requires 4 arguments, but 3 were provided
move_to(Source&& src, Dest& dest, variant_attribute, mpl::false_)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:143:9: note: candidate function template not viable: requires 4 arguments, but 3 were provided
move_to(Source&& src, Dest& dest, variant_attribute, mpl::true_)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:157:9: note: candidate function template not viable: requires 4 arguments, but 3 were provided
move_to(Iterator, Iterator, unused_type, unused_attribute) {}
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:161:9: note: candidate function template not viable: requires 4 arguments, but 3 were provided
move_to(Iterator first, Iterator last, Dest& dest, container_attribute)
^
/usr/local/include/boost/spirit/home/x3/support/traits/move_to.hpp:171:9: note: candidate function template not viable: requires 4 arguments, but 3 were provided
move_to(Iterator first, Iterator last, boost::iterator_range<Iterator>& rng, container_attribute)
^
My goal is to word-split the sentence by whitespace. The word parser returns the first full word into a std::string as expected. Why isn't *word directly compatible with std::vector<std::string>, and what am I supposed to write instead?

Answer 1

I am not sure it actually should work even for the first case.
You are using ASCII version of character parsers (x3::alpha is a synonym for x3::standard::alpha), passed iterator value type is wchar_t, but boost::spirit::char_encoding::standard::ischar() returns false for non-ascii characters.
With x3::standard_wide::alpha it works:
#include <string>
#include <vector>
#include <boost/spirit/home/x3.hpp>
int main() {
namespace x3 = boost::spirit::x3;
std::wstring const str = L"bonjour je suis un petit panda";
auto word = x3::lexeme[+x3::standard_wide::alpha];
std::wstring s;
x3::phrase_parse(begin(str), end(str), word, x3::space, s); // OK
std::vector<std::wstring> v;
x3::phrase_parse(begin(str), end(str), *word, x3::space, v); // OK
}
Another good question should it work with ASCII skipper, and if there a difference between x3::standard::space and x3::standard_wide::space (wide one might consider more characters as white spaces because of Unicode).