1 files changed, 45 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.Core/Messaging/KeyedCollectionDelegate.cs b/src/DotNetOpenAuth.Core/Messaging/KeyedCollectionDelegate.cs
new file mode 100644
index 0000000..c0a08df
--- /dev/null
+++ b/src/DotNetOpenAuth.Core/Messaging/KeyedCollectionDelegate.cs
@@ -0,0 +1,45 @@
+//-----------------------------------------------------------------------
+// <copyright file="KeyedCollectionDelegate.cs" company="Andrew Arnott">
+//     Copyright (c) Andrew Arnott. All rights reserved.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace DotNetOpenAuth.Messaging {
+	using System;
+	using System.Collections.ObjectModel;
+	using System.Diagnostics.Contracts;
+
+	/// <summary>
+	/// A KeyedCollection whose item -&gt; key transform is provided via a delegate
+	/// to its constructor, and null items are disallowed.
+	/// </summary>
+	/// <typeparam name="TKey">The type of the key.</typeparam>
+	/// <typeparam name="TItem">The type of the item.</typeparam>
+	[Serializable]
+	internal class KeyedCollectionDelegate<TKey, TItem> : KeyedCollection<TKey, TItem> {
+		/// <summary>
+		/// The delegate that returns a key for the given item.
+		/// </summary>
+		private Func<TItem, TKey> getKeyForItemDelegate;
+
+		/// <summary>
+		/// Initializes a new instance of the KeyedCollectionDelegate class.
+		/// </summary>
+		/// <param name="getKeyForItemDelegate">The delegate that gets the key for a given item.</param>
+		internal KeyedCollectionDelegate(Func<TItem, TKey> getKeyForItemDelegate) {
+			Requires.NotNull(getKeyForItemDelegate, "getKeyForItemDelegate");
+
+			this.getKeyForItemDelegate = getKeyForItemDelegate;
+		}
+
+		/// <summary>
+		/// When implemented in a derived class, extracts the key from the specified element.
+		/// </summary>
+		/// <param name="item">The element from which to extract the key.</param>
+		/// <returns>The key for the specified element.</returns>
+		protected override TKey GetKeyForItem(TItem item) {
+			ErrorUtilities.VerifyArgumentNotNull(item, "item"); // null items not supported.
+			return this.getKeyForItemDelegate(item);
+		}
+	}
+}