public class Consumable : Item {
    public delegate void ConsumableDelegate(Entity user);
 
    private readonly ConsumableDelegate onUse;
 
    public Consumable(string name, ConsumableDelegate onUse) {
        this.onUse = onUse;
    }
 
    public void Use(Entity user) {
        onUse(user);
    }
}
 
public class ItemDatabase {
    private List<Item> items;
 
    public ItemDatabase() {
        items = new List<Item>();
 
        items.Add(new Consumable("Apple", delegate(Entity user) {
            user.Heal(10);
        }));
    }
}