《STL 원본 분석 》 노트:traits 기술

template 
struct my_is_void
{
    static const bool value = false;
};
  
template <>
struct my_is_void
{
    static const bool value = true;
};
  
cout << my_is_void::value << endl;
cout << my_is_void::value << endl;

template 
void func(Iterator iter)
{
    //                       ？
    *iter var //           。
}
  
//     
template 
void func(Iterator iter)
{
     __func(&*iter);
}

template 
void __func(T* ) 
{
    T var;
}

template 
inline void destory(ForwardIterator first, ForwardIterator last) 
{
    if (is_POD_type(*first))
        ;  //   int POD_type  ，     。
    if (is_no_POD_type(*first))
        for (; first != last; first++) 
            first->~(*first)()    //       ，(*first)      。
}  

//     
struct _true_type  {  };
struct _false_type  {  };
  
//        POD_type
template 
struct _type_traits
{  
    typedef _false_type has_trivial_default_constructor;
    typedef _false_type has_trivial_copy_constructor;
    typedef _false_type has_trivial_assignment_operator;
    typedef _false_type has_trivial_destructor;
    typedef _false_type is_POD_type;
};
  
// char   
template<>
struct _type_traits 
{
    typedef _true_type has_trivial_default_constructor;
    typedef _true_type has_trivial_copy_constructor;
    typedef _true_type has_trivial_assignment_operator;
    typedef _true_type has_trivial_destructor;
    typedef _true_type is_POD_type;
};
  
// int   
template<>
struct _type_traits 
{
    typedef _true_type has_trivial_default_constructor;
    typedef _true_type has_trivial_copy_constructor;
    typedef _true_type has_trivial_assignment_operator;
    typedef _true_type has_trivial_destructor;
    typedef _true_type is_POD_type;
};
  
......  POD         。

//        non trivaial destructor。      
template 
inline void destory(ForwardIterator first, ForwardIterator last) 
{
    /*    _type_traits       */
    typedef typename _type_traits::is_POD_type is_POD_type;
    __destory_aux(first, last, is_POD_type());
}

//    trivial destructor,        
template 
inline void __destory_aux
(ForwardIterator first, ForwardIterator last, _true_type) 
{
}
 
//    non trivial destrouctor，  destroy
template 
inline void __destory_aux(ForwardIterator first, ForwardIterator last,    
_false_type) 
{
    for (; first != last; ++first)
        destory(&*first);
}

// destroy       
template 
inline void destory(T* pointer) 
{
    pointer->~T();
}