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

错误很毛茸茸，但归结为无法调用 move_to，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 returns 将第一个完整单词按预期转换为 std::string。为什么 *word 不直接兼容 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 ASCII 版本的字符解析器（x3::alpha 是 x3::standard::alpha 的同义词），传递的迭代器值类型是 wchar_t，但是 boost::spirit::char_encoding::standard::ischar() returns 非 ascii 字符为 false。

使用 x3::standard_wide::alpha 有效：

#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
}

另一个好问题应该与 ASCII 船长一起使用，如果 x3::standard::space 和 x3::standard_wide::space 之间存在差异（由于 Unicode，宽字符可能会将更多字符视为空格）。

Simple Spirit X3 分词器无法编译，属性不匹配

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

c++

boost-spirit-x3

c++17