RTS Upgrade System

A modifier can be as straightforward as a Consumer, where you would implement it like:

public enum UnitTech {

  IMPROVED_WEAPONS_1(u -> u.damage *= 1.05),
  IMPROVED_WEAPONS_2(u -> u.damage *= 1.15),
  IMPROVED_ARMOR_1(u -> u.defense *= 1.05),
  IMPROVED_ARMOR_2(u -> u.defense *= 1.10);

  private final Consumer<Unit> modifier;

  public UnitTech(Consumer<Unit> modifier){
    this.modifier = Objects.requireNonNull(modifier);
  }

  public final void apply(final Unit unit){
    this.modifier.accept(Objects.requireNonNull(unit));
  }
}

Then an Unit could have a list of modifiers or something like that, where you'd iterate over it and apply them.

Although thinking a bit, some modifiers with bigger scope (ie, "all ranged units have 10% more range), could be stored somewhere in a list of per-player modifiers, and applied when an unit gets created, rather than storing the same modifier in each unit all the time.

Then you'd have per-unit modifiers that are used when say, terrain gets rough, or some unit applies a negative effect on close enemies. Those would get added/removed on a per-unit basis.

A basic "upgrade" can be made of basic inheritance and composition.

A class that holds your object:
class Something {

IMyObject _obj;

}

class First :IMyObject { ....} // This is the "first" level.

class Second : IMyObject {....} // This is the second level.

somewhere in the code:

_obj = new Second(); ...

// Over simplified by you get the point.

A second approach is to use decorators,

class Buff {

private :

Buff mDecoratorBuff;

void Apply(){

// Something

mDecoratorBuff.Apply();

}

}

So you can apply buffs (or upgrades) as you wish, and each applies its own properties.

These are just examples, apply them carefully to your situation.

Thanks for the input guys, I'm currently going with a system a bit similar to what TheChubu suggested, where units have a list of Modifiers that can be added/removed as I see fit and each of them can change values on the unit.

I never used Consumer before so I got lots of implementation ideas by looking at how it works, thanks a lot!