`JsonConvert.DeserializeObject<Model>("{float: NaN}")` fails - json.net

Question

Newtonsoft's Json.Net is obviously capable of deserializing NaN, but I can't seem to coerce it to do it into a provided float field. I get an Unexpected character "N" exception.
In the following code:
using Newtonsoft.Json;
namespace TestNanDeserialize
{
public class Number
{
public float Float;
}
public class Empty
{
}
internal class Program
{
private const string testJson = "{float: NaN}";
private static void Main(string[] args)
{
Succeeds();
Fails();
}
private static void Succeeds()
{
var result = JsonConvert.DeserializeObject<Empty>(testJson);
}
private static void Fails()
{
var result = JsonConvert.DeserializeObject<Number>(testJson);
}
}
}
Succeeds() and Fails() generate two very different call stacks:
Succeeds()
Newtonsoft.Json.dll!Newtonsoft.Json.JsonTextReader.ParseNumberNaN() Line 2299 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonTextReader.ParseValue() Line 1572 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonTextReader.Read() Line 381 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(object newObject, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty member, string id) Line 2331 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, object existingValue) Line 485 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, object existingValue) Line 291 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(Newtonsoft.Json.JsonReader reader, System.Type objectType, bool checkAdditionalContent) Line 167 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonSerializer.DeserializeInternal(Newtonsoft.Json.JsonReader reader, System.Type objectType) Line 823 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonSerializer.Deserialize(Newtonsoft.Json.JsonReader reader, System.Type objectType) Line 802 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject(string value, System.Type type, Newtonsoft.Json.JsonSerializerSettings settings) Line 863 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject<TestNanDeserialize.Empty>(string value, Newtonsoft.Json.JsonSerializerSettings settings) Line 820 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject<TestNanDeserialize.Empty>(string value) Line 757 C#
TestNanDeserialize.exe!TestNanDeserialize.Program.Succeeds() Line 26 C#
TestNanDeserialize.exe!TestNanDeserialize.Program.Main(string[] args) Line 20 C#
Fails()
Newtonsoft.Json.dll!Newtonsoft.Json.JsonTextReader.ReadAsDouble() Line 948 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonContract contract, bool hasConverter) Line 2214 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(object newObject, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty member, string id) Line 2359 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, object existingValue) Line 485 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, object existingValue) Line 291 C#
Newtonsoft.Json.dll!Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(Newtonsoft.Json.JsonReader reader, System.Type objectType, bool checkAdditionalContent) Line 167 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonSerializer.DeserializeInternal(Newtonsoft.Json.JsonReader reader, System.Type objectType) Line 823 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonSerializer.Deserialize(Newtonsoft.Json.JsonReader reader, System.Type objectType) Line 802 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject(string value, System.Type type, Newtonsoft.Json.JsonSerializerSettings settings) Line 863 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject<TestNanDeserialize.Number>(string value, Newtonsoft.Json.JsonSerializerSettings settings) Line 820 C#
Newtonsoft.Json.dll!Newtonsoft.Json.JsonConvert.DeserializeObject<TestNanDeserialize.Number>(string value) Line 757 C#
TestNanDeserialize.exe!TestNanDeserialize.Program.Fails() Line 31 C#
TestNanDeserialize.exe!TestNanDeserialize.Program.Main(string[] args) Line 21 C#
You might think that should be enough for debug this, and perhaps it should, but it doesn't actually make obvious to me what forks were supposed to have occurred differently in all of these layers to make it work.
EDIT: Yes, I'm aware that unquoted NaN is not valid JSON. A stated feature of Json.Net is support for NaN. It obviously is capable of deserializing it, as the code above demonstrates. I'm not certain, however, that it can deserialize into a float field.
NOTE: I've opened a defect for this at: https://github.com/JamesNK/Newtonsoft.Json/issues/908

Answer 1

The cause of your difficulty is that your JSON is invalid -- specifically the symbol NaN needs to be quoted. I.e. the following JSON can be deserialized into your Number class:
{"float": "NaN"}
And the following cannot:
{float: NaN}
Note that there is a setting, FloatFormatHandling.Symbol, that allows NaN to be output without quotes, so it may be earlier versions of Json.NET were able to parse non-quoted NaN strings as float or double. But that seems not to be the case currently. See Serializing NaN results in non-JSON compliant text and also Json.NET 5.0 Release 1: Serializing NaN and Infinity Floating Point Values.
Update 2
I tried deserializing the unquoted JSON string {float: NaN} in various versions of Json.NET:
8.0.2 (current): fails.
7.0.1: succeeds.
3.5: succeeds.
So this may be a regression. You might want to report an issue.
Update
As pointed out by #shannon, there's an inconsistency in Json.NET's extensions to the JSON standard. JToken.Parse("NaN") returns a JValue of type Float, but JsonConvert.DeserializeObject<double>("NaN") throws an exception. It's possible to use this inconsistency to write a converter that handles non-quoted NaN strings:
public class FloatNanConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(float) || objectType == typeof(float?);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.Null)
return null;
var value = JValue.Load(reader);
if (objectType == typeof(float?))
return (float?)value;
else
return (float)value;
}
public override bool CanWrite { get { false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}