Traits

Traits.java

public void one() {
    EntityBuilder builder = Entity.builder();
    builder.makeTrait(EntityTraits.HEALTH, 20); // Stores data
    builder.makeTrait(EntityTraits.ENTITY_TYPE, EntityType.ZOMBIE); // Implements create, destroy, meta functions
    Entity entity = builder.build();
    
    // Damage the entity with a method specific to EntityTraits.HEALTH
    EntityTraits.HEALTH.damage(entity, 5);
}

// EntityBuilder implementation
public class EntityBuilder {
    private static final Object PRESENT = new Object();
    private Object[] traitData = new Object[64];
    
    public void makeTrait(EntityTrait<Void> trait) {
        traitData[trait.id()] = PRESENT; // Very weird? Not sure if we should use a separate bitset or something
    }
    
    public <T> void makeTrait(EntityTrait<T> trait, T object) {
           traitData[trait.id()] = object;
    }
    
    public <T> void ifTraitPresent(EntityTrait<T> trait, UnaryOperator<T> operator) {
        T data = traitData[trait.id()];
        if(data != null) {
            traitData[trait.id()] = operator.apply(data);   
        }
    }
}

// Health implementation
public class EntityTraits {
    public static final EntityTrait<Integer> HEALTH = new EntityTrait<Integer>() {
        public boolean damage(Entity entity, int damage) {
            entity.ifTraitPresent(this, (health) -> health - damage);
        }
        public int id() {
            return 0; // Should probably be handled by some registry?   
        }
    }
}