how to make new C return other static type than C

[deed]

Thanks for your replies. How about this:

interface I {}

interface I1 : I
{
     void setx(int x);
     int getx();
     int getSum();
}

interface I2 : I
{
     void sety(int y);
     int gety();
     int getSum();
}

class Impl : I1, I2
{
     int x, y;

     void setx(int x)   { this.x = x;   }
     int getx()         { return x;     }
     void sety(int y)   { this.y = y;   }
     int gety()         { return y;     }
     int getSum()       { return x + y; }
}

class C
{
     I1 i1;
     I2 i2;
     I currentInterface;

     this()
     {
         i1 = new Impl;    // static type I1
         i2 = csat(I2)i1;  // try to refer to same object through 
i2
         currentInterface = i1;
     }

     void switchInterface()   // Could be private and called 
depending on
                              // internal state
     {
         if (currentInterface == i1) { currentInterface = i2; }
         else                        { currentInterface = i1; }
     }

     /* Direct all method calls to the current interface...
        Perhaps opDispatch?
     */
}

void main()
{
     auto c = new C;
     c.setx(5);       // Should set x to 5 through i1
     c.getSum();      // Should return 5. (5 + 0)
     c.sety(3);       // Should not be possible
     c.switchInterface()   // currentInterface is now i2
     c.setx(10);      // Should not be possible
     c.sety(3);       // Should set y to 8 through i2
     c.getSum();      // Should return 8. (5 + 3)
}


- Could this be possible?
- Will i1 and i2 expose different interfaces to the same object?
- How can a method call on an object be directed to an internal 
object/interface?