c++谷物存档类型专门化不起作用

Question

我正在使用vs2013的谷物1.1.2。

我已经尝试了归档专门化的例子从这里的类型:http://uscilab.github.io/cereal/archive_specialization.html

但是它不会编译错误:

error C2665: 'cereal::make_nvp' : none of the 3 overloads could convert all the argument types ... while trying to match the argument list '(const std::string, const std::string)

我正在尝试编译以下代码，使用示例中的片段:

#include "cerealtypesmap.hpp"
namespace cereal
{
    //! Saving for std::map<std::string, std::string> for text based archives
    // Note that this shows off some internal cereal traits such as EnableIf,
    // which will only allow this template to be instantiated if its predicates
    // are true
    template <class Archive, class C, class A,
        traits::EnableIf<traits::is_text_archive<Archive>::value> = traits::sfinae> inline
    void save(Archive & ar, std::map<std::string, std::string, C, A> const & map)
    {
        for (const auto & i : map)
            ar(cereal::make_nvp<Archive>(i.first, i.second));
    }
    //! Loading for std::map<std::string, std::string> for text based archives
    template <class Archive, class C, class A,
        traits::EnableIf<traits::is_text_archive<Archive>::value> = traits::sfinae> inline
    void load(Archive & ar, std::map<std::string, std::string, C, A> & map)
    {
        map.clear();
        auto hint = map.begin();
        while (true)
        {
            const auto namePtr = ar.getNodeName();
            if (!namePtr)
                break;
            std::string key = namePtr;
            std::string value; ar(value);
            hint = map.emplace_hint(hint, std::move(key), std::move(value));
        }
    }
} // namespace cereal

#include "cerealarchivesjson.hpp"
#include <iostream>
#include <string>
#include <fstream>
int main()
{
    std::stringstream ss;
    {
        cereal::JSONOutputArchive ar(ss);
        std::map<std::string, std::string> filter = { { "type", "sensor" }, { "status", "critical" } };
        ar(CEREAL_NVP(filter));
    }
    std::cout << ss.str() << std::endl;
    {
        cereal::JSONInputArchive ar(ss);
        cereal::JSONOutputArchive ar2(std::cout);
        std::map<std::string, std::string> filter;
        ar(CEREAL_NVP(filter));
        ar2(CEREAL_NVP(filter));
    }
    std::cout << std::endl;
    return 0;
}

注意，如果我删除save()函数重载，它会编译。但我的目标是能够使用map键作为JSON键，所以它是这样的:

{
    "map": {
        "a": 1,
        "b": 2
    },
    "map_not_string": [
        {
            "key": 1,
            "value": 1
        },
        {
            "key": 2,
            "value": 2
        }
    ]
}

Answer 1

我在Cereal的Github上提出了这个问题，并得到了答案:https://github.com/USCiLab/cereal/issues/197

问题是make_nvp的模板化版本，所以

ar(cereal::make_nvp<Archive>(i.first, i.second));

是

ar(cereal::make_nvp(i.first, i.second));

文档已经更新了，所以这应该不再是问题了。