2015_OOP_EnumNestedGeneric_Manager<T>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace World1
{
    // read more about the Constraints https://msdn.microsoft.com/en-us/library/d5x73970.aspx
    class Manager<T> //we can have Constraints (e.g. where T : class)
    {
        private const int CAPACITY = 5;

        private T[] entities;

        private int counter = 0;

        public T this[int i]
        {
            get { return entities[i]; }
            set { entities[i] = value; }
        }

        public Manager()
            : this(CAPACITY)
        { }
        public Manager(int capacity)
        {
            entities = new T[capacity];
        }

        public void AddEntity(T entity) // Push
        {
            if (counter >= entities.Length)
            {
                throw new InvalidOperationException("The stack is full!");
            }
            this.entities[counter] = entity;
            counter++;
        }

        public T RemoveEntity() // <K>
        {
            if (counter == 0) {
                throw new InvalidOperationException("The stack is empty!");
            }
            T temp = entities[counter - 1];
            entities[counter - 1] = default(T);
            counter--;
            return temp;
        }

        public int GetNumberOfEntities()
        {
            return counter;
        }
    }
}