Map of Parent Type and calling child type copy constructor (try two)

Sorry about the duplicate message. I tabbed and then hit space in the
code in my previous message, which I guess sends the message in my news
reader. Anyways...

I'm try to construct a map<int, Shape> so that I can keep a list of
Shapes. Here's a simplified version of my code so far:

class Shape
{
public:
 enum Type {
  CIRCLE,
  SQUARE
 };

 Shape(Type myType, int myInt) :
  myType_(myType), myInt_(myInt) {}

// other standard functions here

private:
 Type myType;
 int myInt_;
};

class Circle : public Shape
{
public:
 Circle(int myInt, int someAddtionalInt) :
  Shape(Shape::CIRCLE, myInt),
  _someAdditionalInt(someAdditionalInt)
 { }

// other standard and shape generic functions here

private:
 int someAdditionalInt;
};

class Square : public Shape
{
public:
 Circle(int myInt, double someDouble) :
  Shape(Shape::SQUARE, myInt),
  _someDouble(someDouble)
 { }

// other standard functions here

private:
 double someDouble;
};

int main(void)
{
 std::map<int, Shape> myList;
 Circle k(101, 102);
 myList[100] = k;
}

This won't compile because map will want to access
operator=(const Shape& rhs) in the class Shape.

Now, I've tried writing operator= a variety of ways. Since I have the
enum Type, I can even tell what type the various Shapes are in the list.
However, I cannot figure out how (if there is a way) to reassign the
subclass part of the object's values from operator= in Shape, or call the
subclass's copy constructor instead of Shape's.

Anyways, I figure I'm probably going about this all wrong (and probably
skating on the fine line of poor class design.) Any
recommendations/insights?

Thanks,

Brandt Dusthimer

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