用作成員屬性C++的模板類型的模板類型輸入

Question

所以我想讓一個模板類成爲一個容器（稍後將操作）一組包含的類，它們也是從模板生成的，並存儲在向量中。

的什麼，我試圖做的是這樣的抽象形式：

template <typename T, size_t numberofapples> 
class Apples { 

    public: 
     Apples(std::vector<T> appleinfo1, std::vector<T> appleinfo2); 

    protected: 
     std::vector<T> apple_stats; 
     std::vector<T> info1, info2; 


}; 

template <typename T, size_t numberofapples> 
Apples<T, numberofapples>::Apples(std::vector<T> appleinfo1, std::vector<T> appleinfo2) : apple_stats(numberofapples, 0){ 
    for (size_t i = 0; i < numberofapples; ++i) { 
     apple_stats[i] = rand(); 
    } 

    info1 = appleinfo1; 
    info2 = appleinfo2; 


} 



template <typename T, typename FruitType, size_t numberoffruitperbranch> 
class Tree { 

    public: 
     Tree(size_t numberofbranches, std::vector<T> commonfruitinfo1, std::vector<T> commonfruitinfo2); 

    protected: 
     std::vector<FruitType<T, numberoffruitperbranch> > branchset; 

};  

template <typename T, typename FruitType, size_t numberoffruitperbranch> 
Tree<T, FruitType, numberoffruitperbranch>::Tree(size_t numberofbranches, std::vector<T> commonfruitinfo1, std::vector<T> commonfruitinfo2) : { 

    typename FruitType<T, numberoffruitperbranch> single_fruit(fruitinfo1, fruitinfo2); 

    branchset.resize(numberofbranches, single_fruit); 
    //in the un-abstracted version that has nothing to do with fruit, I'd then iterate over the vector and run some internal code on each one 
} 

的目標是，我希望能夠做這樣的事情：

Tree<double, Apples, 10> MyFirstTree(5, vectorofdata, secondvectorofdata); 

但是，目前，編譯器告訴我FruitType在構造函數中不是一個有效的模板。實際上，構造函數中的所有內容似乎都超出了範圍，並且被標記，但我無法弄清楚原因。未被引用的版本也有許多其他成員變量和函數，但問題肯定在外部類容器的構造函數中。

我哪裏去錯了/怎麼能做得更好？

編輯：修正了一些編譯器錯誤（我認爲），我注意到了從這個簡單的例子不同，我並沒有在實際應用中

Answer 1

正如@MSN提到的，你需要使用嵌套模板。在你的情況下，他們採取的形式是：

template<typename T, size_t nr, template <typename, size_t> class FruitType> 
class Tree { ... }; 

而且他們用這樣的方式：

Tree<double, 20, Apple> someTree; 

從您提供的代碼真實的例子（VC下編譯++ 2010）：

#include <iostream> 
#include <vector> 

template <typename T, size_t numberofapples> 
class Apples { 

    public: 
     Apples(std::vector<T> appleinfo1, std::vector<T> appleinfo2); 

    protected: 
     std::vector<T> apple_stats; 
     std::vector<T> info1, info2; 


}; 

template <typename T, size_t numberofapples> 
Apples<T, numberofapples>::Apples(std::vector<T> appleinfo1, std::vector<T> appleinfo2) : apple_stats(numberofapples, 0){ 
    for (size_t i = 0; i < numberofapples; ++i) { 
     apple_stats[i] = rand(); 
    } 

    info1 = appleinfo1; 
    info2 = appleinfo2; 


} 



template <typename T, size_t numberoffruitperbranch, template <typename, size_t> class FruitType> 
class Tree { 

    public: 
     Tree(size_t numberofbranches, std::vector<T> commonfruitinfo1, std::vector<T> commonfruitinfo2); 

    protected: 
     std::vector<FruitType<T, numberoffruitperbranch> > branchset; 

};  

template <typename T, size_t numberoffruitperbranch, template <typename, size_t> class FruitType> 
Tree<T, numberoffruitperbranch, FruitType>::Tree(size_t numberofbranches, std::vector<T> commonfruitinfo1, std::vector<T> commonfruitinfo2) { 

    typename FruitType<T, numberoffruitperbranch> single_fruit(commonfruitinfo1, commonfruitinfo2); 

    branchset.resize(numberofbranches, single_fruit); 
    //in the un-abstracted version that has nothing to do with fruit, I'd then iterate over the vector and run some internal code on each one 
}; 

int main() 
{ 
    Tree<double, 10, Apples> someTree(20, std::vector<double>(), std::vector<double>()); 
    return 0; 
} 

Answer 2

你想聲明FruitType爲template template parameter使：

template<..., template <typename, size_t> typename FruitType, ...>