Factory

Factory.cs

public interface IFactory<in TKey, TValue>
    {
        /// <summary>
        /// Registers an item
        /// </summary>
        /// <param name="key">Item to register</param>
        /// <param name="value">The object to be returned</param>
        void Register(TKey key, TValue value);

        /// <summary>
        /// Registers an item
        /// </summary>
        /// <param name="key">Item to register</param>
        /// <param name="constructor">The function to call when creating the item</param>
        void Register(TKey key, Func<TValue> constructor);

        /// <summary>
        /// Creates an instance associated with the key
        /// </summary>
        /// <param name="key">Registered item</param>
        /// <returns>The type returned by the initializer</returns>
        TValue Create(TKey key);
    }

    public class Factory<TKey, TValue> : IFactory<TKey, TValue>
    {
        #region Protected Variables

        /// <summary>
        /// List of constructors/initializers
        /// </summary>
        protected Dictionary<TKey, Func<TValue>> factory = new Dictionary<TKey, Func<TValue>>();

        #endregion

        #region Public Functions

        /// <summary>
        /// Registers an item
        /// </summary>
        /// <param name="key">Item to register</param>
        /// <param name="value">The object to be returned</param>
        public void Register(TKey key, TValue value)
        {
            if (factory.ContainsKey(key))
            {
                factory[key] = () => value;
            }
            else
            {
                factory.Add(key, () => value);
            }
        }

        /// <summary>
        /// Registers an item
        /// </summary>
        /// <param name="key">Item to register</param>
        /// <param name="constructor">The function to call when creating the item</param>
        public void Register(TKey key, Func<TValue> constructor)
        {
            if (factory.ContainsKey(key))
            {
                factory[key] = constructor;
            }
            else
            {
                factory.Add(key, constructor);
            }
        }

        /// <summary>
        /// Creates an instance associated with the key
        /// </summary>
        /// <param name="key">Registered item</param>
        /// <returns>The type returned by the initializer</returns>
        public TValue Create(TKey key)
        {
            if (factory.ContainsKey(key))
            {
                return factory[key]();
            }
            
            throw new KeyNotFoundException(string.Format("Key {0} was not found in the factory - check if it is correct", key));
        }

        #endregion
    }