Merge pull request #1151 from JonHanna/singleton_empty_array

Use singleton for zero-element arrays.

Src/Newtonsoft.Json/JsonReader.cs

@@ -538,7 +538,7 @@ namespace Newtonsoft.Json
                     Guid g;
                     if (s.Length == 0)
                     {
-                        data = new byte[0];
+                        data = CollectionUtils.ArrayEmpty<byte>();
                     }
                     else if (ConvertUtils.TryConvertGuid(s, out g))
                     {

Src/Newtonsoft.Json/JsonTextReader.cs

@@ -146,7 +146,7 @@ namespace Newtonsoft.Json
                     byte[] data;
                     if (_stringReference.Length == 0)
                     {
-                        data = new byte[0];
+                        data = CollectionUtils.ArrayEmpty<byte>();
                     }
                     else if (_stringReference.Length == 36 && ConvertUtils.TryConvertGuid(_stringReference.ToString(), out g))
                     {

Src/Newtonsoft.Json/Linq/JsonPath/QueryExpression.cs

@@ -88,7 +88,7 @@ namespace Newtonsoft.Json.Linq.JsonPath
                 return JPath.Evaluate(pathFilters, root, t, false);
             }
 
-            return new JToken[0];
+            return CollectionUtils.ArrayEmpty<JToken>();
         }
 
         public override bool IsMatch(JToken root, JToken t)

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalReader.cs

@@ -2274,7 +2274,7 @@ namespace Newtonsoft.Json.Serialization
                     return CreateObjectUsingCreatorWithParameters(reader, objectContract, containerMember, objectContract.OverrideCreator, id);
                 }
 
-                newObject = objectContract.OverrideCreator(new object[0]);
+                newObject = objectContract.OverrideCreator(CollectionUtils.ArrayEmpty<object>());
             }
             else if (objectContract.DefaultCreator != null &&
                      (!objectContract.DefaultCreatorNonPublic || Serializer._constructorHandling == ConstructorHandling.AllowNonPublicDefaultConstructor || objectContract.ParameterizedCreator == null))

Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs

@@ -745,7 +745,7 @@ namespace Newtonsoft.Json.Serialization
 
             bool hasWrittenMetadataObject = WriteStartArray(writer, values, contract, member, collectionContract, containerProperty);
 
-            SerializeMultidimensionalArray(writer, values, contract, member, writer.Top, new int[0]);
+            SerializeMultidimensionalArray(writer, values, contract, member, writer.Top, CollectionUtils.ArrayEmpty<int>());
 
             if (hasWrittenMetadataObject)
             {

Src/Newtonsoft.Json/Utilities/CollectionUtils.cs

@@ -29,12 +29,16 @@ using System.Collections.ObjectModel;
 using System.Reflection;
 using System.Text;
 using System.Collections;
+using System.Diagnostics;
 #if NET20
 using Newtonsoft.Json.Utilities.LinqBridge;
 #else
 using System.Linq;
 #endif
 using System.Globalization;
+#if !(NET20 || NET35 || NET40 || PORTABLE40)
+using System.Runtime.CompilerServices;
+#endif
 using Newtonsoft.Json.Serialization;
 
 namespace Newtonsoft.Json.Utilities
@@ -340,9 +344,30 @@ namespace Newtonsoft.Json.Utilities
             }
 
             Array multidimensionalArray = Array.CreateInstance(type, dimensions.ToArray());
-            CopyFromJaggedToMultidimensionalArray(values, multidimensionalArray, new int[0]);
+            CopyFromJaggedToMultidimensionalArray(values, multidimensionalArray, ArrayEmpty<int>());
 
             return multidimensionalArray;
         }
+
+        // 4.6 has Array.Empty<T> to return a cached empty array. Lacking that in other
+        // frameworks, Enumerable.Empty<T> happens to be implemented as a cached empty
+        // array in all versions (in .NET Core the same instance as Array.Empty<T>).
+        // This includes the internal Linq bridge for 2.0.
+        // Since this method is simple and only 11 bytes long in a release build it's
+        // pretty much guaranteed to be inlined, giving us fast access of that cached
+        // array. With 4.5 and up we use AggressiveInlining just to be sure, so it's
+        // effectively the same as calling Array.Empty<T> even when not available.
+#if !(NET20 || NET35 || NET40 || PORTABLE40)
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+#endif
+        public static T[] ArrayEmpty<T>()
+        {
+            T[] array = Enumerable.Empty<T>() as T[];
+            Debug.Assert(array != null);
+            // Defensively guard against a version of Linq where Enumerable.Empty<T> doesn't
+            // return an array, but throw in debug versions so a better strategy can be
+            // used if that ever happens.
+            return array ?? new T[0];
+        }
     }
 }

Src/Newtonsoft.Json/Utilities/DynamicProxy.cs

@@ -37,7 +37,7 @@ namespace Newtonsoft.Json.Utilities
     {
         public virtual IEnumerable<string> GetDynamicMemberNames(T instance)
         {
-            return new string[0];
+            return CollectionUtils.ArrayEmpty<string>();
         }
 
         public virtual bool TryBinaryOperation(T instance, BinaryOperationBinder binder, object arg, out object result)

Src/Newtonsoft.Json/Utilities/DynamicProxyMetaObject.cs

@@ -166,7 +166,7 @@ namespace Newtonsoft.Json.Utilities
 
         private delegate DynamicMetaObject Fallback(DynamicMetaObject errorSuggestion);
 
-        private static readonly Expression[] NoArgs = new Expression[0];
+        private static Expression[] NoArgs => CollectionUtils.ArrayEmpty<Expression>();
 
         private static IEnumerable<Expression> GetArgs(params DynamicMetaObject[] args)
         {

Src/Newtonsoft.Json/Utilities/DynamicUtils.cs

@@ -158,7 +158,7 @@ namespace Newtonsoft.Json.Utilities
 
         public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
         {
-            DynamicMetaObject retMetaObject = _innerBinder.Bind(target, new DynamicMetaObject[] { });
+            DynamicMetaObject retMetaObject = _innerBinder.Bind(target, CollectionUtils.ArrayEmpty<DynamicMetaObject>());
 
             NoThrowExpressionVisitor noThrowVisitor = new NoThrowExpressionVisitor();
             Expression resultExpression = noThrowVisitor.Visit(retMetaObject.Expression);

Src/Newtonsoft.Json/Utilities/ExpressionReflectionDelegateFactory.cs

@@ -87,40 +87,45 @@ namespace Newtonsoft.Json.Utilities
         {
             ParameterInfo[] parametersInfo = method.GetParameters();
 
-            Expression[] argsExpression = new Expression[parametersInfo.Length];
-            IList<ByRefParameter> refParameterMap = new List<ByRefParameter>();
-
-            for (int i = 0; i < parametersInfo.Length; i++)
+            Expression[] argsExpression;
+            IList<ByRefParameter> refParameterMap;
+            if (parametersInfo.Length == 0)
             {
-                ParameterInfo parameter = parametersInfo[i];
-                Type parameterType = parameter.ParameterType;
-                bool isByRef = false;
-                if (parameterType.IsByRef)
+                argsExpression = CollectionUtils.ArrayEmpty<Expression>();
+                refParameterMap = CollectionUtils.ArrayEmpty<ByRefParameter>();
+            }
+            else
+            {
+                argsExpression = new Expression[parametersInfo.Length];
+                refParameterMap = new List<ByRefParameter>();
+
+                for (int i = 0; i < parametersInfo.Length; i++)
                 {
-                    parameterType = parameterType.GetElementType();
-                    isByRef = true;
-                }
-
-                Expression indexExpression = Expression.Constant(i);
-
-                Expression paramAccessorExpression = Expression.ArrayIndex(argsParameterExpression, indexExpression);
-
-                Expression argExpression = EnsureCastExpression(paramAccessorExpression, parameterType, !isByRef);
-
-                if (isByRef)
-                {
-                    ParameterExpression variable = Expression.Variable(parameterType);
-                    refParameterMap.Add(new ByRefParameter
+                    ParameterInfo parameter = parametersInfo[i];
+                    Type parameterType = parameter.ParameterType;
+                    bool isByRef = false;
+                    if (parameterType.IsByRef)
                     {
-                        Value = argExpression,
-                        Variable = variable,
-                        IsOut = parameter.IsOut
-                    });
+                        parameterType = parameterType.GetElementType();
+                        isByRef = true;
+                    }
 
-                    argExpression = variable;
+                    Expression indexExpression = Expression.Constant(i);
+
+                    Expression paramAccessorExpression = Expression.ArrayIndex(argsParameterExpression, indexExpression);
+
+                    Expression argExpression = EnsureCastExpression(paramAccessorExpression, parameterType, !isByRef);
+
+                    if (isByRef)
+                    {
+                        ParameterExpression variable = Expression.Variable(parameterType);
+                        refParameterMap.Add(new ByRefParameter {Value = argExpression, Variable = variable, IsOut = parameter.IsOut});
+
+                        argExpression = variable;
+                    }
+
+                    argsExpression[i] = argExpression;
                 }
-
-                argsExpression[i] = argExpression;
             }
 
             Expression callExpression;

Src/Newtonsoft.Json/Utilities/ReflectionUtils.cs

@@ -90,7 +90,7 @@ namespace Newtonsoft.Json.Utilities
 #if !(PORTABLE40 || PORTABLE)
             EmptyTypes = Type.EmptyTypes;
 #else
-            EmptyTypes = new Type[0];
+            EmptyTypes = CollectionUtils.ArrayEmpty<Type>();
 #endif
         }