Env based appSettings overrides, plus DictionaryAdapter fun

EnvThenConfigSettings.cs

using System;
using System.Configuration;
using System.Collections;

using Castle.Components.DictionaryAdapter;

namespace Demo {
	class MainClass {
		public static void Main (string[] args) {
			var ageString = (string)ConfigurationManager.AppSettings ["Age"];
			var age = int.Parse (ageString);
			Console.WriteLine ("My age is {0}", age);

			var factory = new DictionaryAdapterFactory ();

			var settings1 = factory.GetAdapter<ISomeSettings>(ConfigurationManager.AppSettings);
			Console.WriteLine ("My age is {0}", settings1.Age);

			var settings2 = factory.GetAdapter<ISomeSettings>(new EnvThenConfigSettings());
			Console.WriteLine ("My age is {0}", settings2.Age);

			Environment.SetEnvironmentVariable ("CONFIG_Age", "120");
			Console.WriteLine ("My age is {0}", settings2.Age);
		}
	}


	public interface ISomeSettings {
		string Something { get; set; }
		int Age { get; set; }
	}

	/// <summary>
	/// Allow for Env based override to config's AppSettings.
	/// It is a slimmed down IDictionary implementation. With this usage we only 
	/// care about the index getter, all the rest is no in use so throwing NIEs.
	/// </summary>
	public class EnvThenConfigSettings : IDictionary {
		private const string ENV_PREFIX = "CONFIG_";

		public object this [object index] {
			get {
				var key = index as string;
				if (key == null) {
					throw new ArgumentException ("Only string keys are supported", "index");
				}

				var vars = Environment.GetEnvironmentVariables ();
				var envKeyToLookFor = ENV_PREFIX + key;
				if (vars.Contains (envKeyToLookFor)) {
					return Environment.GetEnvironmentVariable (ENV_PREFIX + index);
				}

				return ConfigurationManager.AppSettings [key];
			}
			set {
				throw new NotImplementedException ();
			}
		}

		bool System.Collections.IDictionary.Contains (object key) {
			throw new NotImplementedException ();
		}
		void System.Collections.IDictionary.Add (object key, object value) {
			throw new NotImplementedException ();
		}
		void System.Collections.IDictionary.Clear () {
			throw new NotImplementedException ();
		}
		System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator () {
			throw new NotImplementedException ();
		}
		void System.Collections.IDictionary.Remove (object key) {
			throw new NotImplementedException ();
		}
		System.Collections.ICollection System.Collections.IDictionary.Keys {
			get {
				throw new NotImplementedException ();
			}
		}
		System.Collections.ICollection System.Collections.IDictionary.Values {
			get {
				throw new NotImplementedException ();
			}
		}
		bool System.Collections.IDictionary.IsReadOnly {
			get {
				throw new NotImplementedException ();
			}
		}
		bool System.Collections.IDictionary.IsFixedSize {
			get {
				throw new NotImplementedException ();
			}
		}
		void System.Collections.ICollection.CopyTo (Array array, int index) {
			throw new NotImplementedException ();
		}
		int System.Collections.ICollection.Count {
			get {
				throw new NotImplementedException ();
			}
		}
		object System.Collections.ICollection.SyncRoot {
			get {
				throw new NotImplementedException ();
			}
		}
		bool System.Collections.ICollection.IsSynchronized {
			get {
				throw new NotImplementedException ();
			}
		}
		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator () {
			throw new NotImplementedException ();
		}
	}
}