【C++模版之旅】项目中一次活用C++模板(traits)的经历 -新注解

class DeleteLong
{
public:
    void operator()(void *p)
    {
        delete static_cast<long*>(p);
    }
};
class DeleteString
{
public:
    void operator()(void *p)
    {
        delete static_cast<string*>(p);
    }
};
class DeleteDouble
{
public:
    void operator()(void *p)
    {
        delete static_cast<double*>(p);
    }
};
 
class ExportData
{
    union
    {
        string * sp;
        long*  lp;
        double* dp;
        void* vp;
 
    };
    enum my_type {SP,LP,DP} types;//change it to object.
    static unordered_map<type_index,my_type> typeMap;
    static vector<function<void(void*)>> deleters;
public:
 
    template <typename T> ExportData(T t)
    {
        if(typeMap.find(typeid(t))==typeMap.end())
            assert(false);
        vp=new T(t);
        types= typeMap[typeid(T)];
    }
    template <typename T> void setData(T t)
    {
        if(typeMap.find(typeid(t))==typeMap.end())
            assert(false);
        (deleters[types])(vp);
        vp=new T(t);
        types=typeMap[typeid(T)];
 
    }
    template <typename T> void getData(T& t)
    {
        if(typeMap[typeid(T)]!=types) assert(false);
        t=*(static_cast<T*>(vp));
    }
    //这里可以改成重载，void getData(long& t){...} void getData(sting& t){....} void getData(double& t){...}调用其他类型则编译错误
 
};
 
unordered_map<type_index,ExportData::my_type> ExportData::typeMap
{
    {typeid(string),ExportData::my_type::SP},
    {typeid(long),ExportData::my_type::LP},
    {typeid(double),ExportData::my_type::DP},
};
vector<function<void(void*)>> ExportData::deleters {DeleteString(),DeleteLong(),DeleteDouble(),};

int main()
{
   
    long i=5;
    long j=0;
    string s="Hello";
    string ss;
    ExportData p(i);
    p.setData(++i);
    p.getData(j);
    p.setData(s);
    p.getData(ss);
    cout<<j<<endl;
    cout<<ss<<endl;
    return 0;
}