Keyed instances of object(s)

program.cs

using System;
using System.ComponentModel.Composition;
using System.Diagnostics;
using System.Linq;
using System.Reflection;

using Autofac;

namespace AFMetadata {
	class Program {
		public const string CONSOLE = "4ACD5288-840A-40A8-81D1-8244BDD60D57";
		public const string TRACE = "EFF42F1C-CD85-41F9-8453-E73DF3B24393";

		static IContainer _container;

		static void Main(string[] args) {
			BuildContainer();

			var sut = _container.Resolve<LogSomeText>();
			sut.Log(CONSOLE, "console text");
			sut.Log(TRACE, "trace text");

			DisposeContainer();

			Console.ReadLine();
		}

		static void BuildContainer() {
			var cb = new ContainerBuilder();
			cb.RegisterType<LogSomeText>().AsSelf();

			cb.RegisterAssemblyTypes(typeof(Program).Assembly)
				.Where(t => t.IsAssignableTo<ILog>() && t.GetCustomAttribute<LogIdAttribute>() != null)
				.Keyed<ILog>(t => t.GetCustomAttribute<LogIdAttribute>().Id);

			cb.Register<Func<string, ILog>>(ctx => {
				var c = ctx.Resolve<IComponentContext>();
				return key => c.ResolveKeyed<ILog>(key);
			}).AsSelf();

			_container = cb.Build();
		}

		static void DisposeContainer() {
			if (_container != null) {
				_container.Dispose();
				_container = null;
			}
		}
	}


	class LogSomeText {
		readonly Func<string, ILog> _sinkFactory;

		public LogSomeText(Func<string, ILog> sinkFactory) {
			_sinkFactory = sinkFactory;
		}

		public void Log(string sinkKey, string info) {
			_sinkFactory.Invoke(sinkKey).Log(info);
		}
	}


	interface ILog {
		bool Log(string data);
	}

	[LogId(Program.CONSOLE)]
	class ConsoleLogger : ILog {
		public bool Log(string data) {
			Console.WriteLine(data);
			return true;
		}
	}

	[LogId(Program.TRACE)]
	class TraceLog : ILog {
		public bool Log(string data) {
			Trace.WriteLine(data);
			return true;
		}
	}

	[MetadataAttribute]
	class LogIdAttribute : Attribute {
		public string Id { get; private set; }

		public LogIdAttribute(string guid) {
			Id = guid;
		}
	}
}