-Performance tweaks

Src/Newtonsoft.Json/Linq/JArray.cs

@@ -39,7 +39,7 @@ namespace Newtonsoft.Json.Linq
   /// </example>
   public class JArray : JContainer, IList<JToken>
   {
-    private readonly IList<JToken> _values = new List<JToken>();
+    private readonly List<JToken> _values = new List<JToken>();
 
     /// <summary>
     /// Gets the container's children tokens.
@@ -188,9 +188,9 @@ namespace Newtonsoft.Json.Linq
     {
       writer.WriteStartArray();
 
-      foreach (JToken token in _values)
+      for (int i = 0; i < _values.Count; i++)
       {
-        token.WriteTo(writer, converters);
+        _values[i].WriteTo(writer, converters);
       }
 
       writer.WriteEndArray();

Src/Newtonsoft.Json/Linq/JConstructor.cs

@@ -36,7 +36,7 @@ namespace Newtonsoft.Json.Linq
   public class JConstructor : JContainer
   {
     private string _name;
-    private readonly IList<JToken> _values = new List<JToken>();
+    private readonly List<JToken> _values = new List<JToken>();
 
     /// <summary>
     /// Gets the container's children tokens.

Src/Newtonsoft.Json/Linq/JObject.cs

@@ -370,9 +370,9 @@ namespace Newtonsoft.Json.Linq
     {
       writer.WriteStartObject();
 
-      foreach (JProperty property in _properties)
+      for (int i = 0; i < _properties.Count; i++)
       {
-        property.WriteTo(writer, converters);
+        _properties[i].WriteTo(writer, converters);
       }
 
       writer.WriteEndObject();

Src/Newtonsoft.Json/Linq/JValue.cs

@@ -511,10 +511,20 @@ namespace Newtonsoft.Json.Linq
     /// <param name="converters">A collection of <see cref="JsonConverter"/> which will be used when writing the token.</param>
     public override void WriteTo(JsonWriter writer, params JsonConverter[] converters)
     {
+      if (converters != null && converters.Length > 0 && _value != null)
+      {
+        JsonConverter matchingConverter = JsonSerializer.GetMatchingConverter(converters, _value.GetType());
+        if (matchingConverter != null)
+        {
+          matchingConverter.WriteJson(writer, _value, new JsonSerializer());
+          return;
+        }
+      }
+
       switch (_valueType)
       {
         case JTokenType.Comment:
-          writer.WriteComment(_value.ToString());
+          writer.WriteComment((_value != null) ? _value.ToString() : null);
           return;
         case JTokenType.Raw:
           writer.WriteRawValue((_value != null) ? _value.ToString() : null);
@@ -525,20 +535,6 @@ namespace Newtonsoft.Json.Linq
         case JTokenType.Undefined:
           writer.WriteUndefined();
           return;
-      }
-
-      JsonConverter matchingConverter;
-      if (_value != null
-        && converters != null
-        && converters.Length > 0
-        && ((matchingConverter = JsonSerializer.GetMatchingConverter(converters, _value.GetType())) != null))
-      {
-        matchingConverter.WriteJson(writer, _value, new JsonSerializer());
-        return;
-      }
-
-      switch (_valueType)
-      {
         case JTokenType.Integer:
           writer.WriteValue(Convert.ToInt64(_value, CultureInfo.InvariantCulture));
           return;