C++ 模板元编程:如何创建和迭代“typedefs"类型列表在模板类中. [英] c++ template metaprogramming: how to create and iterate over list of types that are "typedefs" in template class.

问题描述

我的代码是一个工厂，它根据模板参数的类型创建对象.我想将其扩展为列表"类型.

My code is a factory that creates objects based on types from template parameters. I want to extend this to a "list of" types.

这就是我所拥有的:Algo1 定义了一个类型 indata.FASSubscriberFactory::Create() 返回一个指向 FASSubscriber 的指针.请看这里:

This is what I have: Algo1 defines a type indata. FASSubscriberFactory::Create() returns a pointer to FASSubscriber<Algo1::indata,..> . See here:

struct Algo1  
{
    typedef DataType1 indata;
}

template <class T, class FEED = T::indata, class PROC = typename ProcessorFactory<T>::ptype>
struct FASSubscriberFactory
{
    typedef FASSubscriber<typename PROC , typename FEED > fftype;

    static fftype * Create()
    {
        return new fftype(FASConfig::Data2Feed<FEED>::name, ProcessorFactory<T>::Create());
    }
}

void main() 
{
    auto myFASSubscriber4Algo1 FASSubscriberFactory<Algo1>::Create();
}

这就是我想要的:Algo1 定义了一个 typedef 列表 indata.FASSubscriberFactory::CreateList() 返回指向 FASSubscriber 列表的指针em>foreach 输入 Algo1:indata.参见下面伪代码中的//注释.

This is what I want: Algo1 defines a list of typedefs indata. FASSubscriberFactory::CreateList() returns a pointer to a list of FASSubscriber<Algo1::indata,..> foreach type in Algo1:indata. See //comments in pseudocode below.

struct Algo1 
{
    //Want to define a list of types
    typedef std::list<types> indata = { DataType1, DateType2 }
}

template <class T, class FEEDs = T::indata, class PROC = typename ProcessorFactory<T>::ptype>
struct FASSubscriberFactory
{
    //want to create a list FASSubscribers from list of types T::indata
    typedef list<FASSubscriber<PROC, FEEDs::type> listoffftypes 
    static lisoftypes * CreateList()
    {
        listoffftypes mylot();

        //for each type in FEEDs - want to lopp around list of types
        foreach(feedtype in FEEDs )
        {
            mylot.push(Create<feedtype>());
        }
        return mylot; 
    }

    template <class FEED>
    static fftype * Create()
    {
        typedef FASSubscriber<typename PROC , typename FEED > fftype;

        return new fftype(FASConfig::Data2Feed<FEED>::name, ProcessorFactory<T>::Create());
    }
}

void main() 
{
    auto myListOfFASSubscriber4Algo1 FASSubscriberFactory<Algo1>::Create();
}

我真正想要的是一种定义和迭代模板参数类中定义的类型列表"的方法.看了一下 A. Alexa 的 TYPELISTS，但我没有看到任何循环.

All I really want is a way to define and iterate over a "typelist" which is defined in the template argument class. Took a look at A. Alexa's TYPELISTS, but I didnt see any loops.

谢谢j

推荐答案

我有一种感觉 C++11 中的可变参数模板和 std::tuple 是你想要的，虽然我不是完全确定我明白你在问什么.

I have a feeling variadic templates and std::tuple from C++11 is what you want, although I'm not exactly sure I understand what you're asking.

// returns a tuple of pointers created by a Create for each type in the parameter pack
template<typename... TS>
static std::tuple<TS*...> CreateList() {
    return { Create<TS>()... };
}

请不要用普通的 C++ 代码来描述模板元编程；令人困惑.

Please don't describe template metapogramming in terms of normal C++ code; it is confusing.

例如，如果你这样称呼它:

For instance if you called it like this:

FASSubscriberFactory</* stuff */>::CreateList<int, float, foo, bar>()

它本质上是这样做的:

static std::tuple<int*, float*, foo*, bar*> CreateList() {
    return { Create<int>(), Create<float>(), Create<foo>(), Create<bar>() };
}

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