【转】traits技术及模板偏特化-白红宇

【转】traits技术及模板偏特化

阅读量：5337 次

发布时间：2019-06-15

本文共 1613 字，大约阅读时间需要 5 分钟。

#include 
     
      using namespace std;struct __xtrue_type { }; // define two mark-typestruct __xfalse_type { };class CComplexObject // a demo class{public:     virtual void clone() { cout << "in clone" << endl; }};class CDerivedComplexObject : public CComplexObject // a demo derived class{public:     virtual void clone() { cout << "in derived clone" << endl; }};// A general edtion of Traitstemplate 
      
       struct Traits{     typedef __xfalse_type has_clone_method; // trait 1: has clone method or not? All types defaultly has no clone method.};// Specialized edtion for ComplexObjecttemplate <>struct Traits
       
        {     typedef __xtrue_type has_clone_method;};template 
        
         class XContainer{     template 
         
                   class Impl     {     };     template <>         class Impl <__xtrue_type>     {     public:         void clone(T* pObj)         {             pObj->clone();         }     };     template <>         class Impl <__xfalse_type>     {     public:         void clone(T* pObj)         {         }     };public:     void clone(T* pObj)     {         Impl
          
           
            ::has_clone_method>().clone(pObj); }};void main(){ int* p1 = 0; CComplexObject c2; CComplexObject* p2 = &c2; CDerivedComplexObject c3; CComplexObject* p3 = &c3; // you must point to a derived object by a base-class pointer, //it's a little problem XContainer
            
              n1; XContainer
             
               n2; XContainer
              
                n3; n1.clone(p1); n2.clone(p2); n3.clone(p3);}