Deep clone of System.Random

I'm trying to deep clone an object which contains a System.Random variable. My application must be deterministic and so I need to capture the the random object state. My project is based on .Net Core 2.0.

I'm using some deep clone code from here (How do you do a deep copy of an object in .NET (C# specifically)?) which uses serialization.

The documentation for System.Random is mixed:

Serializable

• https://msdn.microsoft.com/en-us/library/system.random(v=vs.110).aspx

• http://referencesource.microsoft.com/#mscorlib/system/random.cs,bb77e610694e64ca (source code)

Not Serializable

• https://docs.microsoft.com/en-us/dotnet/api/system.random?view=netframework-4.7.1

• https://docs.microsoft.com/en-us/dotnet/api/system.random?view=netcore-2.0

and I get the following error.

System.Runtime.Serialization.SerializationException HResult=0x8013150C Message=Type 'System.Random' in Assembly 'System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e' is not marked as serializable. Source=System.Runtime.Serialization.Formatters

Can System.Random it be cloned in the way I want?

I created a small program to illustrate.

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

namespace RandomTest
{
    class Program
    {
        static void Main(string[] args)
        {
            Container C = new Container();
            Container CopyC = DeepClone(C);
        }

        public static T DeepClone<T>(T obj)
        {
            using(var ms = new MemoryStream())
            {
                var formatter = new BinaryFormatter();
                formatter.Serialize(ms, obj); //<-- error here
                ms.Position = 0;

                return (T)formatter.Deserialize(ms);
            }
        }
    }

    [Serializable]
    public class Container
    {
        public ObjectType AnObject;
        public Container()
        {
            AnObject = new ObjectType();
        }
    }

    [Serializable]
    public class ObjectType
    {
        //[NonSerialized]  // Uncommenting here removes the error
        internal System.Random R;
    }
}

I probably don't need the Container object, but this structure more closely resembles my application.

Making R [NonSerialized] removes the error but I don't get my Random object back after deserialization. I tried re-creating the random object, but it starts a new random sequence and so breaks the deterministic requirement.

You could use JSON.NET to do this.

Use Project | Manage NuGet Packages to add "Newtonsoft.Json" (latest stable version 10.0.3) to your project.

Then you can write a Cloner class that uses Json.NET to clone an object:

public static class Cloner
{
    public static T Clone<T>(T source)
    {
        if (ReferenceEquals(source, null))
            return default(T);

        var settings = new JsonSerializerSettings { ContractResolver = new ContractResolver() };

        return JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(source, settings), settings);
    }

    class ContractResolver : DefaultContractResolver
    {
        protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
        {
            var props = type.GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                .Select(p => base.CreateProperty(p, memberSerialization))
                .Union(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                    .Select(f => base.CreateProperty(f, memberSerialization)))
                .ToList();
            props.ForEach(p => { p.Writable = true; p.Readable = true; });
            return props;
        }
    }
}

Then you can write some code like so:

var inner = new ObjectType {R = new Random(12345)};
var outer = new Container  {AnObject = inner};

var clone = Cloner.Clone(outer);

Console.WriteLine(clone.AnObject.R.Next()); // Prints 143337951
Console.WriteLine(outer.AnObject.R.Next()); // Also prints 143337951