Use EmptyArray<T> instead of new T[0] in System.Composition code

Author: dsplaisted

src/Common/src/Microsoft/Internal/EmptyArray.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Composition;
+using System.Diagnostics;
+using System.Diagnostics.Contracts;
+using System.Globalization;
+using System.Reflection;
+
+namespace Microsoft.Internal
+{
+    internal static class EmptyArray<T>
+    {
+        public static readonly T[] Value = new T[0];
+    }
+}

src/System.Composition.Convention/src/System.Composition.Convention.csproj

@@ -32,6 +32,9 @@
       <DesignTime>True</DesignTime>
       <DependentUpon>CommonStrings.resx</DependentUpon>
     </Compile>
+    <Compile Include="..\..\Common\src\Microsoft\Internal\EmptyArray.cs">
+      <Link>Microsoft\Internal\EmptyArray.cs</Link>
+    </Compile>
     <Compile Include="..\..\Common\src\Microsoft\Internal\Requires.cs">
       <Link>Microsoft\Internal\Requires.cs</Link>
     </Compile>

src/System.Composition.Convention/src/System/Composition/Convention/PartConventionBuilder.cs

@@ -19,7 +19,7 @@ namespace System.Composition.Convention
     /// </summary>
     public class PartConventionBuilder
     {
-        private readonly Type[] _emptyTypeArray = new Type[0];
+        private readonly Type[] _emptyTypeArray = EmptyArray<Type>.Value;
         private static List<Attribute> s_onImportsSatisfiedAttributeList;
         private readonly static List<Attribute> s_importingConstructorList = new List<Attribute>() { new ImportingConstructorAttribute() };
         private readonly static Type s_exportAttributeType = typeof(ExportAttribute);

src/System.Composition.Hosting/src/System.Composition.Hosting.csproj

@@ -39,6 +39,9 @@
       <DesignTime>True</DesignTime>
       <DependentUpon>CommonStrings.resx</DependentUpon>
     </Compile>
+    <Compile Include="..\..\Common\src\Microsoft\Internal\EmptyArray.cs">
+      <Link>Microsoft\Internal\EmptyArray.cs</Link>
+    </Compile>
     <Compile Include="..\..\Common\src\Microsoft\Internal\Requires.cs">
       <Link>Microsoft\Internal\Requires.cs</Link>
     </Compile>

src/System.Composition.Hosting/src/System/Composition/Hosting/CompositionHost.cs

@@ -21,7 +21,7 @@ namespace System.Composition.Hosting
     /// </summary>
     public sealed class CompositionHost : CompositionContext, IDisposable
     {
-        private static readonly string[] s_noBoundaries = new string[0];
+        private static readonly string[] s_noBoundaries = EmptyArray<string>.Value;
 
         private readonly LifetimeContext _rootLifetimeContext;
 

src/System.Composition.Hosting/src/System/Composition/Hosting/Core/ExportDescriptorRegistryUpdate.cs

@@ -16,7 +16,7 @@ internal class ExportDescriptorRegistryUpdate : DependencyAccessor
         private readonly ExportDescriptorProvider[] _exportDescriptorProviders;
         private readonly IDictionary<CompositionContract, UpdateResult> _updateResults = new Dictionary<CompositionContract, UpdateResult>();
 
-        private static readonly CompositionDependency[] s_noDependenciesValue = new CompositionDependency[0];
+        private static readonly CompositionDependency[] s_noDependenciesValue = EmptyArray<CompositionDependency>.Value;
         private static readonly Func<CompositionDependency[]> s_noDependencies = () => s_noDependenciesValue;
 
         private bool _updateFinished;

src/System.Composition.Hosting/src/System/Composition/Hosting/Core/UpdateResult.cs

@@ -12,7 +12,7 @@ namespace System.Composition.Hosting.Core
     // providers, with providers being removed from the list before querying.
     internal class UpdateResult
     {
-        private static readonly ExportDescriptorPromise[] s_noPromises = new ExportDescriptorPromise[0];
+        private static readonly ExportDescriptorPromise[] s_noPromises = EmptyArray<ExportDescriptorPromise>.Value;
 
         private readonly Queue<ExportDescriptorProvider> _remainingProviders;
         private readonly IList<ExportDescriptorPromise> _providedDescriptors = new List<ExportDescriptorPromise>();

src/System.Composition.Hosting/src/System/Composition/Hosting/Providers/ExportFactory/ExportFactoryExportDescriptorProvider.cs

@@ -8,6 +8,7 @@
 using System.Collections.Generic;
 using System.Composition.Hosting.Util;
 using System.Composition.Hosting.Properties;
+using Microsoft.Internal;
 
 namespace System.Composition.Hosting.Providers.ExportFactory
 {
@@ -28,14 +29,14 @@ public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors(Compos
         private static ExportDescriptorPromise[] GetExportFactoryDescriptors<TProduct>(CompositionContract exportFactoryContract, DependencyAccessor definitionAccessor)
         {
             var productContract = exportFactoryContract.ChangeType(typeof(TProduct));
-            var boundaries = new string[0];
+            var boundaries = EmptyArray<string>.Value;
 
             IEnumerable<string> specifiedBoundaries;
             CompositionContract unwrapped;
             if (exportFactoryContract.TryUnwrapMetadataConstraint(Constants.SharingBoundaryImportMetadataConstraintName, out specifiedBoundaries, out unwrapped))
             {
                 productContract = unwrapped.ChangeType(typeof(TProduct));
-                boundaries = (specifiedBoundaries ?? new string[0]).ToArray();
+                boundaries = (specifiedBoundaries ?? EmptyArray<string>.Value).ToArray();
             }
 
             return definitionAccessor.ResolveDependencies("product", productContract, false)

src/System.Composition.Hosting/src/System/Composition/Hosting/Providers/ExportFactory/ExportFactoryWithMetadataExportDescriptorProvider.cs

@@ -10,6 +10,7 @@
 using System.Collections.Generic;
 using System.Composition.Hosting.Providers.Metadata;
 using System.Composition.Hosting.Properties;
+using Microsoft.Internal;
 
 namespace System.Composition.Hosting.Providers.ExportFactory
 {
@@ -33,14 +34,14 @@ public override IEnumerable<ExportDescriptorPromise> GetExportDescriptors(Compos
         private static ExportDescriptorPromise[] GetExportFactoryDescriptors<TProduct, TMetadata>(CompositionContract exportFactoryContract, DependencyAccessor definitionAccessor)
         {
             var productContract = exportFactoryContract.ChangeType(typeof(TProduct));
-            var boundaries = new string[0];
+            var boundaries = EmptyArray<string>.Value;
 
             IEnumerable<string> specifiedBoundaries;
             CompositionContract unwrapped;
             if (exportFactoryContract.TryUnwrapMetadataConstraint(Constants.SharingBoundaryImportMetadataConstraintName, out specifiedBoundaries, out unwrapped))
             {
                 productContract = unwrapped.ChangeType(typeof(TProduct));
-                boundaries = (specifiedBoundaries ?? new string[0]).ToArray();
+                boundaries = (specifiedBoundaries ?? EmptyArray<string>.Value).ToArray();
             }
 
             var metadataProvider = MetadataViewProvider.GetMetadataViewProvider<TMetadata>();

src/System.Composition.TypedParts/src/System.Composition.TypedParts.csproj

@@ -39,6 +39,9 @@
     </ProjectReference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="..\..\Common\src\Microsoft\Internal\EmptyArray.cs">
+      <Link>Microsoft\Internal\EmptyArray.cs</Link>
+    </Compile>
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Properties\Resources.Designer.cs">
       <AutoGen>True</AutoGen>