Conversation function

通过conversation function可以把类转成任意类型的值

 #include <iostream>

 using namespace std;

 class Age
 {
 private:
     int _age;
 public:
     Age(int age) : _age(age) {}
     operator int() const { return _age; }
     operator string() const { return to_string(_age); }
 };

 int main()
 {
     Age myAge();
     Age yourAge();
     if ((myAge - yourAge) > ) {
         cout << "i am older than you" << endl;
     }
     else {
         cout << "i am younger than you" << endl;
     }

     cout << "I am " << myAge << " years old" << endl;
     return ;
 }

jingyg@jingyg:~/share/mytest/cpp_test$ g++ -std=c++ test.cpp
jingyg@jingyg:~/share/mytest/cpp_test$ ./a.out
i am older than you
I am  years old