混叠boost :: variant或std :: variant无法编译

问题描述

当前，我的库使用boost :: optional和boost :: variant.由于C ++ 17已发布，因此我想添加一个选项，使其可以与boost和std一起使用.

Currently my library uses boost::optional and boost::variant. Since C++17 is out, I would like to add an option, that it works with the boost and std.

所以我测试了完整的代码，其中boost可选和variant以及std可选和variant成功.

So I tested the complete code with boost optional and variant and std optional and variant successful.

所以我添加了一个与此相似的头文件:

So I added a header files that is similar to this:

#ifdef USE_BOOST
#include <boost/optional.hpp>
#elif USE_STD
#include <optional>
#endif

namespace Foo {

#ifdef USE_BOOST
template <typename T>
using optional = boost::optional<T>
#elif USE_STD
template <typename T>
using optional = std::optional<T>
#endif

}

一切正常.

然后我为变体添加了类似的内容

Then I added something similar for variant

#ifdef USE_BOOST
#include <boost/variant.hpp>
#elif USE_STD
#include <variant>
#endif

namespace Foo {

#ifdef USE_BOOST
template <typename... T>
using variant = boost::variant<T...>
// similar to the following
#elif USE_STD

template <typename...T>
using variant = std::variant<T...>;

template <class T, class... Types>
constexpr T& get(std::variant<Types...>& v) {
    return std::get<T>(v);
};

template <class T, class... Types>
constexpr T&& get(std::variant<Types...>&& v) {
    return std::get<T>(std::move(v));
};

template <class T, class... Types>
constexpr const T& get(const std::variant<Types...>& v) {
    return std::get<T>(v);
};

template <class T, class... Types>
constexpr const T&& get(const std::variant<Types...>&& v) {
    return std::get<T>(std::move(v));
};

#endif

}

在库中，我现在到处都使用Foo :: optional和Foo :: variant.但是现在所有功能模板，例如

And within the library I use now everywhere Foo::optional and Foo::variant. But now all function templates like

template <typename... Args>
bool bar(const std::tuple<variant<Args,
                                  std::exception_ptr>...>& args)

找不到

了. (c语错误消息:没有匹配的函数可以调用...)

are not found any more. (clang error message: no matching function for call to ...)

经过clang干线和VS 2017 15.6.1预览版测试有什么主意吗?

Tested with clang trunk and VS 2017 15.6.1 PreviewAny idea?

非常感谢！

我的要点

推荐答案

最后解决了问题.这是在VS中lang的错误. GCC编译就可以了. clang和VS的解决方案是使用显式模板参数调用该函数.

Finally problem solved. It is a bug in clang an VS. GCC compiles it fine. The solution for clang and VS is calling the function with explicit template parameters.

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