Re: When is const ref used and when is ref used in an expression?

Hi:

I have the following code:

#include <iostream>

using namspace std;

template<class T>
class Foo
{
public:
   Foo(const T& x) : x_(x) {};
   ~Foo() {};

   operator const T&() const {
     cout << "use const ref" << endl;
     return x_;
   }
   operator T&() { //[1]
     cout << "use ref" << endl; //[2]
     return x_; //[3]
   } //[4]
private:
   T x_;
};

int main()
{
   Foo<int> a(5);

   a += 3; //[5]
   int b = a; //[6]
   cout << a << "," << b << endl; //[7]
}

case 1: When I ran the previous code using MSVC++ 2005 Express
Edition, I got (except the remarks after //):

use ref // debugger confirmed this is due to [5]
use ref // debugger confirmed this is due to [6]
use ref // debugger confirmed this is due to [7]
8,8

I can understand why the non-const reference is used in [5]. But
don't
know why the complier uses the const reference in [6] and [7].

Could some one explain? Thanks.