ECS: removal of group of related components

Question

Currently I'm working with LibGDX and using Ashley for ECS. Everything is fine, until i need to remove groups of related components.

Say we have a player that may use different weapons. For now, in my game a weapon is described by one or more components.

For example we have weapons, each is described by its own components:

weapon1: [ c0, c1, c2 ];
weapon2: [ c3, c4 ];
weapon3: [ c5, c6, c7 ];

It's ok when I want to add a weapon. I know which components are required and can put them to entity. The issue comes when I need to replace one weapon with another.

I can deal with if-else when it's only 3-5 weapons. But what if there are 20?

For now, my idea is to have additional component called WeaponComponent. Which will contain a family (I mean Ashley Family instance) that contains all information i need to remove the unnecessary components. But for me it looks more like a workaround, not a solution.

So, does anybody know how to deal with this? Are there any other approaches?

UPDATE

OK, For now I have tried few implementations. And here is the one that seems to be the best for me. I have combined object-oriented and entity-component designes. The WeaponComponent holds a reference to a Weapon implementation. The Weapon implementations know exaclty which components to attach/remove to/from an entity.

interface Weapon {
    void attachTo(Entity entity);
    void removeFrom(Entity entity);
}
class WeaponComponent {
    private Entity owner;
    private Weapon weapon;
    public void setWeapon(Weapon weapon) {
        if(this.weapon != null)
            this.weapon.removeFrom(owner);
        if(weapon != null) {
            this.weapon = weapon;
            this.weapon.attachTo(owner);
        }
    }
}

So, using this design, changing weapons is very easy now. And I don't have to care what weapon is already attached, and how to remove it: engity.getComponent(WeaponComponent.class).setWeapon(whatEver);.

Answer 1

You can add an enum for the type of component, and add a type attribute to the Component base class.

...
enum EComponentType {
...
    ECT_Weapon,
...
}
...
class Component {
...
    EComponentType _type;

public:
    EComponentType getType() const;
... 
}

Then, you just need to check that attribute

if (component->getType() == EComponentType::ECT_Weapon) {
    entity->remove(component);
}

I have no idea about LibGDX but hope this helps.

Answer 2

If the weapon entity only contains weapon components you could just drop all components using

entity.removeAll();

Or drop the entity from the engine completely and remake with the new components.

Using the remove method to remove component will return null if a component doesn't exists so won't cause any issues if you want to try and remove all weapon components.

entity.remove(component.class);