add singleton options

sdk/core/Azure.Core/src/Serialization/ModelJsonConverter.cs

@@ -30,7 +30,7 @@ public ModelJsonConverter()
         /// </summary>
         /// <param name="format"> The format to serialize to and deserialize from. </param>
         public ModelJsonConverter(ModelSerializerFormat format)
-            : this(new ModelSerializerOptions(format)) { }
+            : this(ModelSerializerOptions.GetOptions(format)) { }
 
         /// <summary>
         /// Initializes a new instance of <see cref="ModelJsonConverter"/>.

sdk/core/Azure.Core/src/Serialization/ModelSerializer.cs

@@ -37,7 +37,7 @@ public static BinaryData Serialize<T>(T model, ModelSerializerOptions? options =
         /// <returns>A <see cref="BinaryData"/> representation of the model in the <see cref="ModelSerializerFormat"/> specified by the <paramref name="format"/></returns>
         public static BinaryData Serialize<T>(T model, ModelSerializerFormat format)
             where T : IModelSerializable<T>
-            => Serialize<T>(model, new ModelSerializerOptions(format));
+            => Serialize<T>(model, ModelSerializerOptions.GetOptions(format));
 
         /// <summary>
         /// Converts the value of a model into a <see cref="BinaryData"/>.
@@ -67,7 +67,7 @@ public static BinaryData Serialize(object model, ModelSerializerOptions? options
         /// <returns>A <see cref="BinaryData"/> representation of the model in the <see cref="ModelSerializerFormat"/> specified by the <paramref name="format"/></returns>
         /// <exception cref="InvalidOperationException">Throws if <paramref name="model"/> does not implement <see cref="IModelSerializable{T}"/>.</exception>
         public static BinaryData Serialize(object model, ModelSerializerFormat format)
-            => Serialize(model, new ModelSerializerOptions(format));
+            => Serialize(model, ModelSerializerOptions.GetOptions(format));
 
         /// <summary>
         /// Converts the <see cref="BinaryData"/> into a <typeparamref name="T"/>.
@@ -92,7 +92,7 @@ public static T Deserialize<T>(BinaryData data, ModelSerializerOptions? options
         /// <exception cref="InvalidOperationException">Throws if <typeparamref name="T"/> does not have a public or internal default constructor.</exception>
         public static T Deserialize<T>(BinaryData data, ModelSerializerFormat format)
             where T : IModelSerializable<T>
-            => Deserialize<T>(data, new ModelSerializerOptions(format));
+            => Deserialize<T>(data, ModelSerializerOptions.GetOptions(format));
 
         /// <summary>
         /// Converts the <see cref="BinaryData"/> into a <paramref name="returnType"/>.
@@ -120,7 +120,7 @@ public static object Deserialize(BinaryData data, Type returnType, ModelSerializ
         /// <exception cref="InvalidOperationException">Throws if <paramref name="returnType"/> does not implement <see cref="IModelSerializable{T}"/>.</exception>
         /// <exception cref="InvalidOperationException">Throws if <paramref name="returnType"/> does not have a public or internal default constructor.</exception>
         public static object Deserialize(BinaryData data, Type returnType, ModelSerializerFormat format)
-            => Deserialize(data, returnType, new ModelSerializerOptions(format));
+            => Deserialize(data, returnType, ModelSerializerOptions.GetOptions(format));
 
         /// <summary>
         /// Converts an <see cref="IModelJsonSerializable{T}"/> into a <see cref="BinaryData"/>.
@@ -149,7 +149,7 @@ public static BinaryData ConvertToBinaryData(IModelJsonSerializable<object> mode
         /// <param name="format">The <see cref="ModelSerializerFormat"/> to use.</param>
         /// <returns>A binary representation of the serialized model.</returns>
         public static BinaryData ConvertToBinaryData(IModelJsonSerializable<object> model, ModelSerializerFormat format)
-            => ConvertToBinaryData(model, new ModelSerializerOptions(format));
+            => ConvertToBinaryData(model, ModelSerializerOptions.GetOptions(format));
 
         private static IModelSerializable<object> GetInstance(Type returnType)
         {

sdk/core/Azure.Core/src/Serialization/ModelSerializerOptions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Collections.Generic;
 
 namespace Azure.Core.Serialization
 {
@@ -10,10 +11,19 @@ namespace Azure.Core.Serialization
     /// </summary>
     public class ModelSerializerOptions
     {
+        private static readonly IReadOnlyDictionary<ModelSerializerFormat, ModelSerializerOptions> _singletonMap = new Dictionary<ModelSerializerFormat, ModelSerializerOptions>()
+        {
+            { ModelSerializerFormat.Json, new ModelSerializerOptions(ModelSerializerFormat.Json, true) },
+            { ModelSerializerFormat.Wire, new ModelSerializerOptions(ModelSerializerFormat.Wire, true) }
+        };
+
         /// <summary>
         /// Default options for serializing models into the format the Azure serivce is expecting.
         /// </summary>
-        public static readonly ModelSerializerOptions DefaultWireOptions = new ModelSerializerOptions(ModelSerializerFormat.Wire, true);
+        public static readonly ModelSerializerOptions DefaultWireOptions = _singletonMap[ModelSerializerFormat.Wire];
+
+        internal static ModelSerializerOptions GetOptions(ModelSerializerFormat format)
+            => _singletonMap.TryGetValue(format, out ModelSerializerOptions? options) ? options! : new ModelSerializerOptions(format);
 
         private bool _isFrozen;
         private Func<Type, ObjectSerializer>? _genericTypeSerializerCreator;

sdk/core/Azure.Core/tests/ModelSerializerOptionsTests.cs

@@ -0,0 +1,66 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using Azure.Core.Serialization;
+using NUnit.Framework;
+
+namespace Azure.Core.Tests
+{
+    internal class ModelSerializerOptionsTests
+    {
+        [Test]
+        public void ValidatePropertyIsFrozen() => ValidateFrozenInstance(ModelSerializerOptions.DefaultWireOptions);
+
+        [Test]
+        public void AllInstancesInMapShouldBeFrozen()
+        {
+            Dictionary<ModelSerializerFormat, ModelSerializerOptions> optionsDictionary = typeof(ModelSerializerOptions)
+                .GetField("_singletonMap", BindingFlags.NonPublic | BindingFlags.Static)
+                .GetValue(null) as Dictionary<ModelSerializerFormat, ModelSerializerOptions>;
+            foreach (var frozen in optionsDictionary.Values)
+            {
+                ValidateFrozenInstance(frozen);
+            }
+        }
+
+        public void ValidateFrozenInstance(ModelSerializerOptions frozen)
+        {
+            Assert.Throws<InvalidOperationException>(() => frozen.GenericTypeSerializerCreator = type => null);
+        }
+
+        [Test]
+        public void NewInstanceShouldNotBeFrozen()
+        {
+            ModelSerializerOptions nonFrozen = new ModelSerializerOptions();
+            Assert.DoesNotThrow(() => nonFrozen.GenericTypeSerializerCreator = type => null);
+        }
+
+        [Test]
+        public void MapAndStaticPropertySameObject()
+        {
+            Assert.IsTrue(ReferenceEquals(ModelSerializerOptions.DefaultWireOptions, ModelSerializerOptions.GetOptions(ModelSerializerFormat.Wire)));
+        }
+
+        [Test]
+        public void MapShouldReturnSingletons()
+        {
+            Assert.IsTrue(ReferenceEquals(ModelSerializerOptions.GetOptions(ModelSerializerFormat.Wire), ModelSerializerOptions.GetOptions(ModelSerializerFormat.Wire)));
+            Assert.IsTrue(ReferenceEquals(ModelSerializerOptions.GetOptions(ModelSerializerFormat.Json), ModelSerializerOptions.GetOptions(ModelSerializerFormat.Json)));
+        }
+
+        [Test]
+        public void MapShouldHaveRightValues()
+        {
+            var options = ModelSerializerOptions.GetOptions(ModelSerializerFormat.Wire);
+            Assert.AreEqual(ModelSerializerFormat.Wire, options.Format);
+            Assert.IsNull(options.GenericTypeSerializerCreator);
+
+            options = ModelSerializerOptions.GetOptions(ModelSerializerFormat.Json);
+            Assert.AreEqual(ModelSerializerFormat.Json, options.Format);
+            Assert.IsNull(options.GenericTypeSerializerCreator);
+        }
+    }
+}

sdk/core/Azure.Core/tests/ModelSerializerTests.cs

@@ -10,16 +10,6 @@ namespace Azure.Core.Tests.ModelSerializationTests
 {
     public class ModelSerializerTests
     {
-        [Test]
-        public void ValidateFrozenInstance()
-        {
-            ModelSerializerOptions frozen = ModelSerializerOptions.DefaultWireOptions;
-            ModelSerializerOptions nonFrozen = new ModelSerializerOptions();
-
-            Assert.Throws<InvalidOperationException>(() => frozen.GenericTypeSerializerCreator = type => null);
-            Assert.DoesNotThrow(() => nonFrozen.GenericTypeSerializerCreator = type => null);
-        }
-
         [Test]
         public void ValidateErrorIfUnknownDoesntExist()
         {