-Added readonly to structs

Src/Newtonsoft.Json/Linq/JEnumerable.cs

@@ -39,7 +39,7 @@ namespace Newtonsoft.Json.Linq
     /// Represents a collection of <see cref="JToken"/> objects.
     /// </summary>
     /// <typeparam name="T">The type of token.</typeparam>
-    public struct JEnumerable<T> : IJEnumerable<T>, IEquatable<JEnumerable<T>> where T : JToken
+    public readonly struct JEnumerable<T> : IJEnumerable<T>, IEquatable<JEnumerable<T>> where T : JToken
     {
         /// <summary>
         /// An empty collection of <see cref="JToken"/> objects.

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

@@ -33,6 +33,8 @@ namespace Newtonsoft.Json.Linq.JsonPath
 {
     internal class JPath
     {
+        private static readonly char[] FloatCharacters = new[] {'.', 'E', 'e'};
+
         private readonly string _expression;
         public List<PathFilter> Filters { get; }
 
@@ -601,7 +603,7 @@ namespace Newtonsoft.Json.Linq.JsonPath
                     {
                         string numberText = sb.ToString();
 
-                        if (numberText.IndexOfAny(new[] { '.', 'E', 'e' }) != -1)
+                        if (numberText.IndexOfAny(FloatCharacters) != -1)
                         {
                             bool result = double.TryParse(numberText, NumberStyles.Float | NumberStyles.AllowThousands, CultureInfo.InvariantCulture, out var d);
                             value = d;
@@ -688,7 +690,7 @@ namespace Newtonsoft.Json.Linq.JsonPath
                             resolvedChar = currentChar;
                             break;
                         default:
-                            throw new JsonException(@"Unknown escape character: \" + _expression[_currentIndex]);
+                            throw new JsonException(@"Unknown escape character: \" + currentChar);
                     }
 
                     sb.Append(resolvedChar);

Src/Newtonsoft.Json/Serialization/CamelCasePropertyNamesContractResolver.cs

@@ -30,7 +30,7 @@ using Newtonsoft.Json.Utilities;
 
 namespace Newtonsoft.Json.Serialization
 {
-    internal struct ResolverContractKey : IEquatable<ResolverContractKey>
+    internal readonly struct ResolverContractKey : IEquatable<ResolverContractKey>
     {
         private readonly Type _resolverType;
         private readonly Type _contractType;

Src/Newtonsoft.Json/Utilities/ConvertUtils.cs

@@ -248,7 +248,7 @@ namespace Newtonsoft.Json.Utilities
 #endif
         }
 
-        internal struct TypeConvertKey : IEquatable<TypeConvertKey>
+        internal readonly struct TypeConvertKey : IEquatable<TypeConvertKey>
         {
             public Type InitialType { get; }
 

Src/Newtonsoft.Json/Utilities/DictionaryWrapper.cs

@@ -482,7 +482,7 @@ namespace Newtonsoft.Json.Utilities
             }
         }
 
-        private struct DictionaryEnumerator<TEnumeratorKey, TEnumeratorValue> : IDictionaryEnumerator
+        private readonly struct DictionaryEnumerator<TEnumeratorKey, TEnumeratorValue> : IDictionaryEnumerator
         {
             private readonly IEnumerator<KeyValuePair<TEnumeratorKey, TEnumeratorValue>> _e;
 

Src/Newtonsoft.Json/Utilities/LinqBridge.cs

@@ -2991,10 +2991,10 @@ namespace Newtonsoft.Json.Utilities.LinqBridge
   }
 
   [Serializable]
-  internal struct Tuple<TFirst, TSecond> : IEquatable<Tuple<TFirst, TSecond>>
+  internal readonly struct Tuple<TFirst, TSecond> : IEquatable<Tuple<TFirst, TSecond>>
   {
-    public TFirst First { get; private set; }
-    public TSecond Second { get; private set; }
+    public TFirst First { get; }
+    public TSecond Second { get; }
 
     public Tuple(TFirst first, TSecond second)
       : this()

Src/Newtonsoft.Json/Utilities/ReflectionUtils.cs

@@ -1109,7 +1109,7 @@ namespace Newtonsoft.Json.Utilities
         }
     }
 
-    internal struct TypeNameKey : IEquatable<TypeNameKey>
+    internal readonly struct TypeNameKey : IEquatable<TypeNameKey>
     {
         internal readonly string AssemblyName;
         internal readonly string TypeName;

Src/Newtonsoft.Json/Utilities/StringReference.cs

@@ -27,7 +27,7 @@ using System;
 
 namespace Newtonsoft.Json.Utilities
 {
-    internal struct StringReference
+    internal readonly struct StringReference
     {
         private readonly char[] _chars;
         private readonly int _startIndex;