source: TFP-WebServer/WebServer/src/LiveData/EntityFilterList.cs

using System;
using System.Collections.Generic;

namespace Webserver.LiveData {
        public abstract class EntityFilterList<T> where T : Entity {
                public void Get (List<T> _list) {
                        _list.Clear ();
                        try {
                                List<Entity> entities = GameManager.Instance.World.Entities.list;
                                for (int i = 0; i < entities.Count; i++) {
                                        Entity entity = entities [i];

                                        T element = predicate (entity);
                                        if (element != null) {
                                                _list.Add (element);
                                        }
                                }
                        } catch (Exception e) {
                                Log.Exception (e);
                        }
                }

                public int GetCount () {
                        int count = 0;
                        try {
                                List<Entity> entities = GameManager.Instance.World.Entities.list;
                                for (int i = 0; i < entities.Count; i++) {
                                        Entity entity = entities [i];

                                        if (predicate (entity) != null) {
                                                count++;
                                        }
                                }
                        } catch (Exception e) {
                                Log.Exception (e);
                        }

                        return count;
                }

                protected abstract T predicate (Entity _e);
        }
}