Add basic Lazy<T> type

5 files changed, 93 insertions, 1 deletions

diff --git a/LibGit2Sharp.Tests/EpochFixture.cs b/LibGit2Sharp.Tests/EpochFixture.cs
index e82c97d6..4dd4e0ab 100644
--- a/LibGit2Sharp.Tests/EpochFixture.cs
+++ b/LibGit2Sharp.Tests/EpochFixture.cs
@@ -1,5 +1,4 @@
 using System;
-using System.Globalization;
 using LibGit2Sharp.Core;
 using NUnit.Framework;
 
diff --git a/LibGit2Sharp.Tests/LazyFixture.cs b/LibGit2Sharp.Tests/LazyFixture.cs
new file mode 100644
index 00000000..42c7e4a7
--- /dev/null
+++ b/LibGit2Sharp.Tests/LazyFixture.cs
@@ -0,0 +1,42 @@
+using System;
+using LibGit2Sharp.Core;
+using NUnit.Framework;
+using LibGit2Sharp.Tests.TestHelpers;
+
+namespace LibGit2Sharp.Tests
+{
+    [TestFixture]
+    public class LazyFixture
+    {
+        [Test]
+        public void CanReturnTheValue()
+        {
+            var lazy = new Lazy<int>(() =>  2);
+            lazy.Value.ShouldEqual(2);
+        }
+
+        [Test]
+        public void IsLazilyEvaluated()
+        {
+            int i = 0;
+
+            var evaluator = new Func<int>(() => ++i);
+
+            var lazy = new Lazy<int>(evaluator);
+            lazy.Value.ShouldEqual(1);
+        }
+
+        [Test]
+        public void IsEvaluatedOnlyOnce()
+        {
+            int i = 0;
+
+            var evaluator = new Func<int>(() => ++i);
+
+            var lazy = new Lazy<int>(evaluator);
+
+            lazy.Value.ShouldEqual(1);
+            lazy.Value.ShouldEqual(1);
+        }
+    }
+}
\ No newline at end of file
diff --git a/LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj b/LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj
index 8924209d..ddf10dfc 100644
--- a/LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj
+++ b/LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj
@@ -42,6 +42,7 @@
     <Reference Include="System.Core" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="LazyFixture.cs" />
     <Compile Include="TestHelpers\BaseFixture.cs" />
     <Compile Include="BlobFixture.cs" />
     <Compile Include="BranchFixture.cs" />
diff --git a/LibGit2Sharp/Core/Lazy.cs b/LibGit2Sharp/Core/Lazy.cs
new file mode 100644
index 00000000..77ceff8d
--- /dev/null
+++ b/LibGit2Sharp/Core/Lazy.cs
@@ -0,0 +1,49 @@
+using System;
+
+namespace LibGit2Sharp.Core
+{
+    /// <summary>
+    /// Provides support for lazy initialization.
+    /// </summary>
+    /// <typeparam name="TType">Specifies the type of object that is being lazily initialized.</typeparam>
+    public class Lazy<TType>
+    {
+        private readonly Func<TType> evaluator;
+        private TType value;
+        private bool hasBeenEvaluated;
+        private readonly object padLock = new object();
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Lazy{TType}"/> class.
+        /// </summary>
+        /// <param name="evaluator"></param>
+        public Lazy(Func<TType> evaluator)
+        {
+            Ensure.ArgumentNotNull(evaluator, "evaluator");
+
+            this.evaluator = evaluator;
+        }
+
+        /// <summary>
+        /// Gets the lazily initialized value of the current instance.
+        /// </summary>
+        public TType Value { get { return Evaluate(); } }
+
+        private TType Evaluate()
+        {
+            if (!hasBeenEvaluated)
+            {
+                lock (padLock)
+                {
+                    if (!hasBeenEvaluated)
+                    {
+                        value = evaluator();
+                        hasBeenEvaluated = true;
+                    }
+                }
+            }
+
+            return value;
+        }
+    }
+}
\ No newline at end of file
diff --git a/LibGit2Sharp/LibGit2Sharp.csproj b/LibGit2Sharp/LibGit2Sharp.csproj
index dedb29d5..e38804e6 100644
--- a/LibGit2Sharp/LibGit2Sharp.csproj
+++ b/LibGit2Sharp/LibGit2Sharp.csproj
@@ -60,6 +60,7 @@
     <Compile Include="Core\GitSignature.cs" />
     <Compile Include="Core\GitTime.cs" />
     <Compile Include="Core\IntPtrExtensions.cs" />
+    <Compile Include="Core\Lazy.cs" />
     <Compile Include="Core\NativeMethods.cs" />
     <Compile Include="Core\ObjectSafeWrapper.cs" />
     <Compile Include="Core\PosixPathHelper.cs">