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(35);
    Age yourAge(21);
    if ((myAge - yourAge) > 0) {
        cout << "i am older than you" << endl;
    }
    else {
        cout << "i am younger than you" << endl;
    }

    cout << "I am " << myAge << " years old" << endl;
    return 0;
}

jingyg@jingyg:~/share/mytest/cpp_test$ g++ -std=c++11 test.cpp 
jingyg@jingyg:~/share/mytest/cpp_test$ ./a.out 
i am older than you
I am 35 years old