在类内部声明模板化函数(基于容器类型)，在模板类外部定义模板化函数(基于容器类型)

declaration of templated function (over container type) inside class and definition of it outside a template class over container type-

本文关键字：于容器 类型 函数 定义 外部 内部 声明      更新时间：2023-10-16

关于我这里的问题

我有一个模板类如下: 
//traits.hpp
 namespace traits {
  typedef std::vector <int>  container_t;
  typedef std::set <int>    container_t2;
  typedef std::list <int>    container_t3;
};
//FOO.hpp
class FOO { 
  public:
    static int a; static int b; static int c; 
 };
 int FOO::a = 10;  int FOO::b = 20;  int FOO::c = 30;

// BAR.hpp
using namespace traits;
template <class FOO>
class BAR {
  public:
   BAR : m_a (FOO::a), m_b (FOO::b), m_c (FOO::c)  {  } 

  // I can happily do this. ===>> VALID
  template <template <typename, typename> class ContainerT, typename ValueT>
  void Initialize(ContainerT <ValueT, std::allocator <ValueT>>&  container) 
  {
    typedef ContainerT<ValueT, std::allocator <ValueT>> type;
    int id = 0;
    for (auto& i : container)
       i = id++;
  }

  void DO_THIS () 
  { 
     Initialize (my_container)
  }
 private:
  container_t  my_container;
   int m_a, m_b, m_c;
}
 // in main.
  BAR <FOO> bar_object;
  bar_object.DO_THIS ();    // calls the initialize function. which is fine.

我只是想这样做:在类之外定义Initialize模板函数。

using namespace traits;
template <class FOO>
class BAR {
  public:
   BAR : m_a (FOO::a), m_b (FOO::b), m_c (FOO::c)  {  } 
  // prototype of Initialize 
  void Initialize ( **?? what to put here ??** ); 
  // I cant put container_t&  BECAUSE  I have several containers such as  
  // set/vector/list. 
  // If I want to initialize the container using set / vector / list, the prototype
  // will be incorrect.
  // i cant declare a prototype for each container type. 
  void DO_THIS () 
  { 
     Initialize (my_container1);
     Initialize (my_container2);
  }
 private:
  container_t1  my_container1;
  container_t2  my_container2
   int m_a, m_b, m_c;
 };

  // unable to define the function properly outside the class. 
  // gives template errors
  template <template <typename, typename> class ContainerT, typename ValueT>
  void Initialize(ContainerT <ValueT, std::allocator <ValueT>>&  container) 
  {
    typedef ContainerT<ValueT, std::allocator <ValueT>> type;
    int id = 0;
    for (auto& i : container)
       i = id++;
  }

我可以在类内部编写函数模板Initialize()而不会出现任何错误。但我想把它写在外面。对我之前帖子的评论很有帮助，但我不得不改变我的实现

总之我想要的是:1. 在类之外的容器类型上编写泛型函数模板。2. 这个函数在类中的原型是什么?

请建议

与之前完全相同，只是省略了正文:

template <class FOO>
class BAR {
  public:
   BAR : m_a (FOO::a), m_b (FOO::b), m_c (FOO::c)  {  } 
  template <template <typename, typename> class ContainerT, typename ValueT>
  void Initialize(ContainerT <ValueT, std::allocator <ValueT>>&  container);
  // ... rest unchanged
};
// Definition outside:
template <class FOO>  // for the class
template <template <typename, typename> class ContainerT, typename ValueT>  // for the function
void BAR<FOO>::Initialize<ContainerT, ValueT>(ContainerT <ValueT, std::allocator <ValueT>>&  container)
{
  // same as before
}
相关文章：