C / C++ / MFC

// this class uses a policy to turn off observers
template <typename CharType,
          class ObserverPolicy
         >
class YourAlgorithmClass
{
public:
    // ...
    void AddObserver( Observer* pObs );
    // more observer mehtods depending on your needs
protected:
    // the overloads. The compiler will choose the right overload for
    // CharType. In the overload for wchar_t, you can convert the message
    // to a char string and call the other overload.
    //
    // You don't even need the overloads here, but you can 
    // place the overloads in the observer class
    // it's a matter of your own taste.
    void SendMessageToObservers(char* pszMessage);
    void SendMessageToObservers(wchar_t* pszMessage);

private:
    std::vector<Observer*> m_Observers;
};

// In the implementation you can use the ObserverPolicy to turn off and on
// the observers.
template <typename CharType, class ObserverPolicy>
void YourAlgorithmClass<CharType, ObserverPolicy>::SendMessageToObservers(char* pszMessage)
{   // the compiler will use this method depending on the policy.
    // if the method returns false, the function does nothing and the 
    // compiler should omit the call
    // 
    // note that I used 'should' since I don't don't if every compiler 
    // is this smart
    if( !ObserverPolicy::UseObservers() )
        return; 

    // notify observers here
}

// ...
// A policy class could look like this:
class UseObservers
{
public:
    static bool UseObservers() { return true; }
}

// or for no observers
class DontUseObservers
{
public:
    static bool UseObservers() { return false; }
}

// Get the selected color from the CColorDialog.
CColorDialog dlg;
if (dlg.DoModal() == IDOK)
{
   COLORREF color = dlg.GetColor();
   TRACE("RGB value of the selected color - red = %u, 
      green = %u, blue = %u\n",
      GetRValue(color), GetGValue(color), GetBValue(color));
}

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown