c++ - 具有可变参数类型的模板多可变继承

Question

我需要多次继承以下类，将可变参数作为模板参数。

template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalMap
{
//private
public:

    void RegisterSlot(SignalAddress pSignalFunc, ISlotInvoker<ArgTypes...>* pSlotInvoker)
    {
        //implementation
    }
};

到目前为止，我可以扩展一个参数包并获得多个类特化，但函数只接受一个参数。

template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalStorage : public ISignalMap<SignalDispatcherClass, ArgTypes>...
{
};

///////
ISignalStorage<SignalA, int, double, bool> iss; 

现在，这允许我使用单个参数（int、double 或 bool - 相应地）注册插槽函数。我需要的是看起来像这样的东西：

ISignalStorage<SignalA, <int, double, bool>, <int, int>, <const char*>> iss;

到目前为止，我一直在研究其他问题，其中一个似乎与该主题有些接近，尽管我未能实施或理解它。希望有一种更简单的方法（可变参数模板模板）

补充： 代码示例

struct IDummySlot
{
    void FuncDbl(double)
    {}
    void FuncInt(int)
    {}
    void FuncIntDbl(int, double)
    {}
};

template <class ... Args>
struct ISlotInvoker
{};

template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalMap
{
public:

    void RegisterSlot(void(IDummySlot::*pSignalFunc)(ArgTypes...), ISlotInvoker<ArgTypes...>* pSlotInvoker)
    {
        return;
    }
};

template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalStorage : public ISignalMap<SignalDispatcherClass, ArgTypes>...
{
};


int main()
{
    ISignalStorage<IDummySlot, int, double> iss;

    ISlotInvoker<int> slot_int;
    ISlotInvoker<double> slot_double;
    ISlotInvoker<int, double> slot_intDouble;

    //iss.RegisterSlot(&IDummySlot::FuncInt, &slot_int); //ambigous
    /*Appears to be that I didn't test it, I just saw that inheritance worked as I expected, but didn't try to invoke*/

    return 0;
}

标签： c++c++17variadic-templatesmultiple-inheritance

Answer 1

这里的基本问题是没有语法可以从单个参数包中“挤压”多个可变参数包。

在这种情况下，通常的方法是使用 astd::tuple来包装每个单独的参数包，并从这些元组中制作一个参数包：

    ISignalStorage<foo, std::tuple<int, double>, std::tuple<double, int>> a;

然后，将每个参数包从使用特化中解开变得很简单std::tuple：

#include <tuple>


template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalMap
{
};

// Take a class, and a tuple. Give me an ISignalMap for the class, and
// what's in the tuple.

template<typename cl, typename tuple_t> struct tuple_expansion;

template<typename cl, typename ...tuple_types>
struct tuple_expansion<cl, std::tuple<tuple_types...>> {

    typedef ISignalMap<cl, tuple_types...> type;
};

// Syntactic sugar.    
template<typename cl, typename tuple_t>
using tuple_expansion_t=typename tuple_expansion<cl, tuple_t>::type;

// And a variadic parameter pack of tuples...

template <class SignalDispatcherClass, class ... ArgTypes>
class ISignalStorage : public tuple_expansion_t<SignalDispatcherClass,
                        ArgTypes>...
{
};

class foo;

void bar()
{

    // Note the syntax: pass each "inner" parameter pack wrapped into a
    // tuple.
    ISignalStorage<foo, std::tuple<int, double>, std::tuple<double, int>> a;

    ISignalMap<foo, int, double> &b=a;
    ISignalMap<foo, double, int> &c=a;
}