Delphi class variables - oop

Question

I have the following code:
// irrelevant code ...
type
Zombie = class
private
...
Age : Integer;
Alive : Boolean;
TotalDeadZombies, TotalZombieAge : Double;
public
...
procedure ZombieGrow();
procedure CheckIfDead();
...
Function AvgLife() : Double;
end;
procedure Zombie.ZombieGrow();
begin
...
if (Alive = false) then
begin
TotalDeadZombies := TotalDeadZombies + 1;
TotalZombieAge := TotalZombieAge + Age;
end;
end;
procedure Zombie.CheckIfDead();
begin
if Random(100) < 20 then
Alive := False;
end;
function Zombie.AvgLife() : Double;
begin
Result := TotalZombieAge / TotalDeadZombie;
end;
The problem I have is I want to display the average age of dead zombies. This would be done via something like :
Write('Average age '+Floattostr(Round(AvgLife)))
However, this is called in another class (not shown here), and from my understanding of OOP, it would require me to specify an instantiated object, e.g zombies[1].AvgLife if they were stored in, say, a Zombies[] array (just an example).
Is there a way of making it so the variables TotalDeadZombies and TotalZombieAge are not tied to any instantiated zombies, but rather to a class variable that I can then just call AvgLife somehow? Is it as simple as just making them global variables? Or can it be done another way?

Answer 1

You just have to declare the variables as class var; then they belong to the class, and not to a particular instance of a class.
type
TZombie = class
public
class var TotalDeadZombies, TotalZombieAge: Double;
end;
You can access these like TZombie.TotalDeadZombies. Similarly, there are class methods, class properties, etc.
Have a look at the official documentation.