c++ - Simple Spirit X3 分词器无法编译，属性不匹配

Question

我正在尝试使用 Spirit X3 解析器来处理命令行工具的输出，但遇到了问题。我已将它们缩小到一个我不理解其行为的最小示例:

#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

错误非常多，但归结为无法调用 move_to ，其中 IIUC 是属性类型不匹配的症状。

/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)
        ^

我的目标是用空格对句子进行分词。 word解析器将第一个完整单词返回到 std::string正如预期的那样。为什么不是 *word直接兼容 std::vector<std::string> ，我应该写什么？

Answer 1

我不确定它是否真的适用于第一种情况。

您正在使用字符解析器的 ASCII 版本(x3::alpha 是 x3::standard::alpha 的同义词)，传递的迭代器值类型是 wchar_t，但 boost::spirit::char_encoding::standard::ischar() 对非 ascii 字符返回 false。

使用 x3::standard_wide::alpha 可以工作:

#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
}

另一个很好的问题是它应该与 ASCII skipper 一起使用吗？由于 Unicode，人们可能会将更多字符视为空格)。