使用boost升压变型::输出::精神::因果报应 [英] Output of a boost::variant type using boost::spirit::karma

问题描述

我试图输出参数，它们可以是单个参数或参数的向量。下面code不，我想它做什么：

I'm trying to output parameters, they can either be a single parameter or a vector of parameters. The following code does not what I'd like it to do:

#include <iostream>
#include <string>
#include <boost/variant.hpp>
#include <boost/spirit/include/karma.hpp>
namespace karma = boost::spirit::karma;

typedef std::vector<int> ParameterList;
typedef boost::variant<int, ParameterList> Parameter;

main()
{
    using karma::int_;
    using karma::eol;
    using karma::lit;

    std::string generated;
    std::back_insert_iterator<std::string> sink(generated);

    karma::rule<std::back_insert_iterator<std::string>, ParameterList()> parameterListRule = int_ % lit(", ");
    karma::rule<std::back_insert_iterator<std::string>, Parameter()> parameterRule = (int_ | parameterListRule) << eol;

    karma::generate(sink, parameterRule, 1); // Works
    karma::generate(sink, parameterRule, ParameterList{1, 2}); // Doesn't work
    std::cout << generated << "\n";
}

（真正的code有其他类型的参数，而不仅仅是诠释，我不能只是让一切参数列表。）

(The real code has other types of parameters, not just int, and I cannot just make everything a ParameterList.)

我不明白如何使这项工作，特别是因为用于分析一个类似的建筑我使用boost ::精神::气为工作正常。

I do not quite understand how to make this work, in particular since an analogous construction for parsing works fine for me using boost::spirit::qi.

推荐答案

在你的第二个电话你没有把一个变种在生成，但规则期望之一。

In your second call you didn't put a variant in the generator, but the rule expects one.

#include <iostream>
#include <string>
#include <boost/variant.hpp>
#include <boost/spirit/include/karma.hpp>
namespace karma = boost::spirit::karma;

typedef std::vector<int> ParameterList;
typedef boost::variant<int, ParameterList> Parameter;

main()
{
    using karma::int_;
    using karma::eol;
    using karma::lit;

    std::string generated;
    std::back_insert_iterator<std::string> sink(generated);

    karma::rule<std::back_insert_iterator<std::string>, ParameterList()> parameterListRule = int_ % lit(", ");
    karma::rule<std::back_insert_iterator<std::string>, Parameter()> parameterRule = (int_ | parameterListRule) << eol;

    karma::generate(sink, parameterRule, 1); // Works
    // use variant here:
    Parameter test(ParameterList{1, 2});
    karma::generate(sink, parameterRule, test);
    std::cout << generated << "\n";
}

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