From Mechanism to Method: Function Follows Form

Listing 4: Smart function pointer copying

class function_ptr
{
public:
    ...
    function_ptr(const function_ptr &other)
      : body(other.body ? other.body->clone() : 0)
    {
    }
    function_ptr &operator=(const function_ptr &rhs)
    {
        callable *old_body = body;
        body = rhs.body ? rhs.body->clone() : 0;
        delete old_body;
        return *this;
    }
    ...
};