spirit x3 如何将向量添加到 AST

Question

我正在尝试解析文件并将数据复制到 class 对象内的向量中。我以员工为例并将其修改为我正在尝试做的事情。正在解析的文件看起来像这样（但更多行）...

1 0.2 0.3 0.4

我已经添加了一个向量来构造 employee 并且在 phrase_parse 行上遇到断言失败。

static assertion failed: Attribute does not have the expected size.
static_assert(
^

我有点认为预期大小与矢量有关。想想我哪里出错了？

namespace client {
    namespace ast {

    struct employee
    {
        int id;
        std::vector<double> coords;
    };

    using boost::fusion::operator<<;
}}

BOOST_FUSION_ADAPT_STRUCT(
    client::ast::employee,
    (int, id)
    (std::vector<double>, coords)
)

namespace client
{
    namespace parser
    {
        namespace x3 = boost::spirit::x3;
        namespace ascii = boost::spirit::x3::ascii;

        using x3::int_;
        using x3::double_;

        x3::rule<class employee, ast::employee> const employee = "employee";
        auto const employee_def =
             int_ >> double_ >> double_ >> double_;
        BOOST_SPIRIT_DEFINE(employee)
    }
}

int main()
{
    using boost::spirit::x3::ascii::space;
    using client::parser::employee;

    string fil("test-file.in");

    mapped_file_source map(fil);
    istringstream iss(map.data());
    map.close();

    client::ast::employee emp;

    boost::spirit::istream_iterator iter(iss >> noskipws), eof;

    phrase_parse(iter, eof, employee, space, emp);
    // failure on above line
}

Answer 1

根据文档，double_ >> double_ >> double_ 合成了双倍、双倍、双倍的融合序列（因此 fusion::tuple<double, double, double> 或 fusion::list<double, double, double> 等） .

你想要一个向量，所以你需要一个重复解析器（运算符）

repeat 指令将执行 repeat(3) [double_]
Kleene star (operator *) 或 plus (operator +) 很有趣（但没有限制）
列表运算符 (operator %) 也是无界的，但接受定界符（例如 double_ % ','

在这种情况下，我会采取另一种方式：对语法使用适当的 AST：

Live On Coliru

struct coord {
    double x,y,z;
};

struct employee
{
    int id;
    coord coords;
};

调整它们比您使用的老式方法更简单：

BOOST_FUSION_ADAPT_STRUCT(client::ast::coord, x, y, z)
BOOST_FUSION_ADAPT_STRUCT(client::ast::employee, id, coords)

解析器很干净

auto const coord_def = double_ >> double_ >> double_;
auto const employee_def = int_ >> coord;

完整演示：

Live On Coliru

#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/include/support_istream_iterator.hpp>
#include <boost/fusion/adapted/struct.hpp>
#include <iostream>

namespace client {
    namespace ast {

    struct coord {
        double x,y,z;
    };

    struct employee
    {
        int id;
        coord coords;
    };

    using boost::fusion::operator<<;
}}

BOOST_FUSION_ADAPT_STRUCT(client::ast::coord, x, y, z)
BOOST_FUSION_ADAPT_STRUCT(client::ast::employee, id, coords)

namespace client
{
    namespace parser
    {
        namespace x3 = boost::spirit::x3;
        namespace ascii = boost::spirit::x3::ascii;

        using x3::int_;
        using x3::double_;

        x3::rule<class employee, ast::coord>    const coord    = "coord";
        x3::rule<class employee, ast::employee> const employee = "employee";

        auto const coord_def = double_ >> double_ >> double_;
        auto const employee_def = int_ >> coord;

        BOOST_SPIRIT_DEFINE(employee, coord);
    }
}

int main()
{
    using boost::spirit::x3::ascii::space;
    using client::parser::employee;

    std::istringstream iss("1 0.2 0.3 0.4");

    client::ast::employee emp;

    boost::spirit::istream_iterator iter(iss >> std::noskipws), eof;

    bool ok = phrase_parse(iter, eof, employee, space, emp);
    if (ok)
        std::cout << "parsed: " 
             << emp.id       << " "
             << emp.coords.x << " "
             << emp.coords.y << " "
             << emp.coords.z << "\n";
}

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