仿SGI STL的traits技法

首先是iterator traits，这个是用来萃取迭代器的特性的

 #ifndef _STL_ITERATOR_H_
 #define _STL_ITERATOR_H_

 #include <cstddef>
 /*
 **    iterator_traits<Iterator>  ----> 负责萃取迭代器的特性
 */
 namespace zstd
 {
     struct inpt_iterator_tag{};
     struct outpt_iterator_tag{};
     struct forward_iterator_tag :public inpt_iterator_tag {};
     struct bidirectional_iterator_tag :public forward_iterator_tag {};
     struct random_access_iterator_tag :public bidirectional_iterator_tag {};

     template<class Category, class T, class Distance = ptrdiff_t,
             class Pointer = T*, class Reference = T&>
     struct iterator
     {
         typedef Category    iterator_category;
         typedef T            value_type;
         typedef Distance    difference_type;
         typedef Pointer        pointer;
         typedef Reference    reference;
     };

     template<class Iterator>
     struct iterator_traits
     {
         typedef typename Iterator::Category        iterator_category;
         typedef typename Iterator::T            value_type;
         typedef typename Iterator::Distance        difference_type;
         typedef typename Iterator::Pointer        pointer;
         typedef typename Iterator::Reference     reference;
     };
     template<class T>
     struct iterator_traits<T*>
     {
         typedef random_access_iterator_tag     iterator_category;
         typedef T                             value_type;
         typedef ptrdiff_t                     difference_type;
         typedef T*                            pointer;
         typedef T&                             reference;
     };
     template<class T>
     struct iterator_traits<const T*>
     {
         typedef random_access_iterator_tag     iterator_category;
         typedef T                             value_type;
         typedef ptrdiff_t                     difference_type;
         typedef const T*                    pointer;
         typedef const T&                     reference;
     };

     template<class Iterator>
     inline typename Iterator::iterator_category
     iterator_category(const Iterator& It)
     {
         typedef typename Iterator::iterator_category category;
         return category();
     }
     template<class Iterator>
     inline typename Iterator::value_type*
     value_type(const Iterator& It)
     {
         return static_cast<typename iterator_traits<Iterator>::value_type*>();
     }
     template<class Iterator>
     inline typename Iterator::difference_type*
     difference_type(const Iterator& It)
     {
         return static_cast<typename iterator_traits<Iterator>::difference_type*>();
     }
 }
 #endif

然后是type traits，这个是用来萃取c++语言型别（type）的特性的

 #ifndef _TYPE_TRAITS_H_
 #define _TYPE_TRAITS_H_

 /*
 **    _type_traits<T>  ----> 负责萃取型别T的特性
 */
 #include <iostream>
 using namespace std;
 namespace zstd
 {
     struct _true_type { void print(){ cout << "_true_type" << endl; } };
     struct _false_type { void print(){ cout << "_false_type" << endl; } };

     template<class T>
     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;
     };

     template<>
     struct _type_traits<bool>
     {
         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;
     };
     template<>
     struct _type_traits<char>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned char>
     {
         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;
     };
     template<>
     struct _type_traits<signed char>
     {
         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;
     };
     template<>
     struct _type_traits<wchar_t>
     {
         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;
     };
     template<>
     struct _type_traits<short>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned short>
     {
         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;
     };
     template<>
     struct _type_traits<int>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned int>
     {
         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;
     };
     template<>
     struct _type_traits<long>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned long>
     {
         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;
     };
     template<>
     struct _type_traits<long long>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned long long>
     {
         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;
     };
     template<>
     struct _type_traits<float>
     {
         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;
     };
     template<>
     struct _type_traits<double>
     {
         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;
     };
     template<>
     struct _type_traits<long double>
     {
         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;
     };

     template<class T>
     struct _type_traits<T*>
     {
         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;
     };
     template<class T>
     struct _type_traits<const T*>
     {
         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;
     };
     template<>
     struct _type_traits<char*>
     {
         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;
     };
     template<>
     struct _type_traits<unsigned char*>
     {
         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;
     };
     template<>
     struct _type_traits<signed char*>
     {
         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;
     };
     template<>
     struct _type_traits<const char*>
     {
         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;
     };
     template<>
     struct _type_traits<const unsigned char*>
     {
         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;
     };
     template<>
     struct _type_traits<const signed char*>
     {
         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;
     };
 }
 #endif