Practical Template Programming - Learn C++ for Game Development - page 204

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This works because the stringLength passed to each SDBMCalculator template is used to index into
the string with 1 subtracted. Then as we start with the length of the string calling the SDBMCalculate
method recursively down until we hit 1, we access the characters in the string in order.
Template metaprogramming can be hard to understand when you're just learning C++. Don't worry
about that too much for now. Come back to this code in the future when you're ready to tackle some
more template metaprogramming.
We'll update our QuitOption to use messages now that we can create a unique ID for the QuitEvent .
Using an Event to Quit the Game
Using an event to quit the game is relatively straightforward. To begin we'll update the
QuitOption::Evaluate method to send the QuitEvent . Listing 21-20 shows how this is done.
Listing 21-20. Updating QuitOption::Evaluate
namespace
{
constexpr int QuitEvent = SDBMCalculator< >::CalculateValue("QuitEvent");
}
void QuitOption::Evaluate(Player& player)
{
SendEvent(QuitEvent);
}
You can finally see the benefit of using the friend functions with the EventManager , as sending the
QuitEvent is just a single line of code!
The main change required is to inherit the Game class from EventHandler as shown in Listing 21-21.
Listing 21-21. Updating the Game Class
class Game
: public EventHandler
{
private:
static const unsigned int m_numberOfRooms = 4;
using Rooms = std::array<Room, m_numberOfRooms>;
Rooms m_rooms;
Player m_player;