CODEWITHSUNDEEP
c#generics
Denzil
Denzil

Reputation: 704

C#, generic way to access different lists within a class

I have a class of 3 different linked lists (for saving the entities in a game I'm working on). The lists are all of objects with the same base type, but I keep them separate for processing reasons. Note that IEntity, IObject and IUndead all inherited from IEntity.

public class EntityBucket
{
    public LinkedList<IEntity> undeadEntities;
    public LinkedList<IEntity> objects;
    public LinkedList<IEntity> livingEntities;

    public EntityBucket()
    {
        undeadEntities = new LinkedList<IEntity>();
        objects = new LinkedList<IEntity>();
        livingEntities = new LinkedList<IEntity>();
    }

    public LinkedList<IEntity> GetList(IObject e)
    {
        return objects;
    }

    public LinkedList<IEntity> GetList(IUndead e)
    {
        return undeadEntities;
    }

    public LinkedList<IEntity> GetList(ILiving e)
    {
        return livingEntities;
    }

}

I have 3 methods for retrieving each of the lists, currently based on their parameters. The fact that there are 3 is fine, since I know each list will in some way or another require its own accessor. Passing an instantiated object is not ideal though, as I may want to retrieve a list somewhere without having an object of similar type at hand. Note that the object here is not even used in the GetList methods, they are only there to determine which version to use. Here is an example where I have an instantiated object at hand:

public void Delete(IUndead e, World world)
{

     .....
     LinkedList<IEntity> list = buckets[k].GetList(e);
     .....
}

I don't like this current implementation as I may not always have an instantiated object at hand (when rendering the entities for example). I was thinking of doing it generically but I'm not sure if this is possible with what I want to do. With this I also need 3 Delete methods (and 3 of any other, such as add and so forth) - one for each type, IUndead, IObject and ILiving. I just feel that this is not the right way of doing it.

I'll post what I have tried to do so far on request, but my generics is rather bad and I feel that it would be a waste for anyone to read this as well.

Finally, performance is very important. I'm not prematurely optimizing, I am post-optimizing as I have working code already, but need it to go faster. The getlist methods will be called very often and I want to avoid any explicit type checking.

Upvotes: 5

Views: 305

Answers (4)

Amy B
Amy B

Reputation: 110071

How about a better implementation to go with that better interface?

public class EntityBucket
{
  public LinkedList<IEntity> Entities;

  public IEnumerable<T> GetEntities<T>() where T : IEntity
  {
    return Entities.OfType<T>();
  }

}


List<IUndead> myBrainFinders = bucket.GetEntities<IUndead>().ToList();

With this implementation, the caller better add each item to the right list(s). That was a requirement for your original implementation, so I figure it's no problem.

public class EntityBucket
{
  Dictionary<Type, List<IEntity>> entities = new Dictionary<Type, List<IEntity>>();

  public void Add<T>(T item) where T : IEntity
  {
    Type tType = typeof(T);
    if (!entities.ContainsKey(tType))
    {
      entities.Add(tType, new List<IEntity>());
    }
    entities[tType].Add(item);
  }

  public List<T> GetList<T>() where T : IEntity
  {
    Type tType = typeof(T);
    if (!entities.ContainsKey(tType))
    {
      return new List<T>();
    }
    return entities[tType].Cast<T>().ToList();
  }

  public List<IEntity> GetAll()
  {
    return entities.SelectMany(kvp => kvp.Value)
      .Distinct() //to remove items added multiple times, or to multiple lists
      .ToList();
  }

}

Upvotes: 1

Stu Peacock
Stu Peacock

Reputation: 9

Seems to me you could just implement a Dictionary of named LinkedList's and refer to them by name or enum.

That way adding or removing lists is just an implementation issue and no separate class to deal with.

Upvotes: 0

ean5533
ean5533

Reputation: 8994

How about something like the following?

public LinkedList<IEntity> GetList(Type type) {
    if (typeof(IUndead).IsAssignableFrom(type)) return undeadEntities;
    if (typeof(ILiving).IsAssignableFrom(type)) return livingEntities;
    if (typeof(IObject).IsAssignableFrom(type)) return objects;
}

Then you would call it like this:

var myUndeads = GetList(typeof(IUndead));
var myLivings = GetList(typeof(ILiving));
// etc

The same type of logic could be implemented in your deletes, add, and other methods, and you never need a concrete instance of an object to access them.

The IsAssignableFrom logic handles subclassing just fine (i.e. you could have a CatZombie, which derives from Zombie, which implements IUndead, and this would still work). This means you still only have to create one Delete method, something like the following:

public void Delete(IEntity e, World world) {
    if (typeof(IUndead).IsAssignableFrom(type)) undeadEntities.Remove(e);
    if (typeof(ILiving).IsAssignableFrom(type)) livingEntities.Remove(e);
    if (typeof(IObject).IsAssignableFrom(type)) objects.Remove(e);
}

EDIT: I noticed your comment on zmbq's answer regarding performance; this is definitely NOT fast. If you need high performance, use an enum-style approach. Your code will be more verbose and require more maintenance, but you'll get much better performance.

Upvotes: 1

zmbq
zmbq

Reputation: 39013

So you want a better interface, because, as you said, passing an unnecessary object to GetList just to figure out its type makes little sense.

You could do something like:

public List<IEntity> GetList<T>() : where T:IEntity
{
    if(typeof(T)==typeof(IUndead)) return undedEntities;
    // and so on
}

And you'll have to call it like this: GetList<IUndead>();

I think an enum is a better idea here:

enum EntityTypes { Undead, Alive, Object };
public List<IEntity> GetList(EntityTypes entityType) { ... }

It's cleaner and makes more sense to me.

EDIT: Using generics is actually not that simple. Someone could call GetList a Zombie type, which implements IUndead, and then you'll have to check for interface implementations. Someone could even pass you a LiveZombie which implements both IUndead and IAlive. Definitely go with an enum.

Upvotes: 3

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