使用不可移动/不可复制的类型创建 hana 元组

Question

我正在努力思考伟大的 boost::hana 并试图弄清楚如何翻译一些老派的元组代码。

也许它有点特殊，但我有既不可复制也不可移动的类型，想将它们打包到一个容器中。思考政策设计...

我想我只是不知道如何在值世界中创建 hana 元组。我尝试的方法不起作用，因为 make<Tuple>(CompT{}...) 需要可复制或至少可移动的类型。

所以很可能这不是实现它的方法。或者这是 hana 的限制？

谢谢！

struct NonMoveable
{
    NonMoveable() = default;
    NonMoveable(const NonMoveable& other) = delete;

    int val;
};

struct Simple { int val; };

template <typename ...CompT>
struct OldSchoolContainer
{
    template <int I>
    auto& getComponent()
    {
        return std::get<I>(components);
    }

    std::tuple<CompT...> components;
};

template <typename ...CompT>
struct HanaContainer
{
    using Args_t = decltype(make<Tuple>(CompT{}...));

    template <int I>
    auto& getComponent()
    {
        return components[int_<I>];
    }

    Args_t components;
};

int main()
{
    OldSchoolContainer<Simple> simpleOsc;
    static_assert(std::is_same<Simple&, decltype(simpleOsc.getComponent<0>())>::value, "");

    HanaContainer<Simple> simpleHanaC;
    static_assert(std::is_same<Simple&, decltype(simpleHanaC.getComponent<0>())>::value, "");


    OldSchoolContainer<NonMoveable> nonmoveableOsc;
    static_assert(std::is_same<NonMoveable&, decltype(nonmoveableOsc.getComponent<0>())>::value, "");

    // !!! this does not compile because hana's tuple closure needs to either move or copy
    HanaContainer<NonMoveable> nonmoveableHanaC;
    static_assert(std::is_same<NonMoveable&, decltype(nonmoveableHanaC.getComponent<0>())>::value, "");

    return 0;
}

Answer 1

您可以使用几乎与 std::tuple 完全相同的 hana::_tuple<...> 类型。因此，以下工作：

#include <boost/hana/integral_constant.hpp>
#include <boost/hana/tuple.hpp>
#include <tuple>
#include <type_traits>
namespace hana = boost::hana;


struct NonMoveable
{
    NonMoveable() = default;
    NonMoveable(const NonMoveable& other) = delete;

    int val;
};

struct Simple { int val; };

template <typename ...CompT>
struct HanaContainer
{
    template <int I>
    auto& getComponent()
    {
        return components[hana::int_<I>];
    }

    hana::_tuple<CompT...> components;
};

int main()
{
    HanaContainer<Simple> simpleHanaC;
    static_assert(std::is_same<Simple&, decltype(simpleHanaC.getComponent<0>())>::value, "");

    HanaContainer<NonMoveable> nonmoveableHanaC;
    static_assert(std::is_same<NonMoveable&, decltype(nonmoveableHanaC.getComponent<0>())>::value, "");

    return 0;
}

使用不可移动/不可复制的类型创建 hana 元组

Create hana tuple with unmovable / noncopyable types

c++

c++14

boost-hana