First as enumerable extensions

SVN: trunk@5317

Author: fabiomaulo

src/NHibernate.Test/NHibernate.Test.csproj

@@ -581,6 +581,7 @@
     <Compile Include="TypesTest\XmlDocClass.cs" />
     <Compile Include="TypesTest\XmlDocTypeFixture.cs" />
     <Compile Include="UtilityTest\EnumerableExtensionsTests\AnyExtensionTests.cs" />
+    <Compile Include="UtilityTest\EnumerableExtensionsTests\FirstExtensionTests.cs" />
     <Compile Include="UtilityTest\ReflectionHelperIsMethodOfTests.cs" />
     <Compile Include="UtilityTest\ReflectionHelperTest.cs" />
     <Compile Include="Linq\RegresstionTests.cs" />

src/NHibernate.Test/UtilityTest/EnumerableExtensionsTests/FirstExtensionTests.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections;
+using NHibernate.Util;
+using NUnit.Framework;
+using SharpTestsEx;
+
+namespace NHibernate.Test.UtilityTest.EnumerableExtensionsTests
+{
+	public class FirstExtensionTests
+	{
+		[Test]
+		public void WhenNullThenThenThrows()
+		{
+			Executing.This(() => ((IEnumerable)null).First()).Should().Throw<ArgumentNullException>();
+		}
+
+		[Test]
+		public void WhenHasElementsThenReturnFirst()
+		{
+			(new[] { 2, 1 }).First().Should().Be(2);
+		}
+
+		[Test]
+		public void WhenEmptyThenThrowsInvalidOperation()
+		{
+			Executing.This(() => (new object[0]).First()).Should().Throw<InvalidOperationException>();
+		}
+	}
+}

src/NHibernate/Util/EnumerableExtensions.cs

@@ -21,6 +21,33 @@ public static bool Any(this IEnumerable source)
 			return false;
 		}
 
+		public static object First(this IEnumerable source)
+		{
+			if (source == null)
+			{
+				throw new ArgumentNullException("source");
+			}
+			IList collection = source as IList;
+			if (collection != null)
+			{
+				if (collection.Count > 0)
+				{
+					return collection[0];
+				}
+			}
+			else
+			{
+				using (DisposableEnumerator enumerator = source.GetDisposableEnumerator())
+				{
+					if (enumerator.MoveNext())
+					{
+						return enumerator.Current;
+					}
+				}
+			}
+			throw new InvalidOperationException("Sequence contains no elements");
+		}
+
 		private static DisposableEnumerator GetDisposableEnumerator(this IEnumerable source)
 		{
 			return new DisposableEnumerator(source);