How do I clone a generic list in C#?

Question

I have a generic list of objects in C#, and wish to clone the list. The items within the list are cloneable, but there doesn\'t seem to be an option to do list.Clone()

Answer 1

Another thing: you could use reflection. If you'll cache this properly, then it'll clone 1,000,000 objects in 5.6 seconds (sadly, 16.4 seconds with inner objects).

[ProtoContract(ImplicitFields = ImplicitFields.AllPublic)]
public class Person
{
       ...
      Job JobDescription
       ...
}

[ProtoContract(ImplicitFields = ImplicitFields.AllPublic)]
public class Job
{...
}

private static readonly Type stringType = typeof (string);

public static class CopyFactory
{
    static readonly Dictionary ProperyList = new Dictionary();

    private static readonly MethodInfo CreateCopyReflectionMethod;

    static CopyFactory()
    {
        CreateCopyReflectionMethod = typeof(CopyFactory).GetMethod("CreateCopyReflection", BindingFlags.Static | BindingFlags.Public);
    }

    public static T CreateCopyReflection(T source) where T : new()
    {
        var copyInstance = new T();
        var sourceType = typeof(T);

        PropertyInfo[] propList;
        if (ProperyList.ContainsKey(sourceType))
            propList = ProperyList[sourceType];
        else
        {
            propList = sourceType.GetProperties(BindingFlags.Public | BindingFlags.Instance);
            ProperyList.Add(sourceType, propList);
        }

        foreach (var prop in propList)
        {
            var value = prop.GetValue(source, null);
            prop.SetValue(copyInstance,
                value != null && prop.PropertyType.IsClass && prop.PropertyType != stringType ? CreateCopyReflectionMethod.MakeGenericMethod(prop.PropertyType).Invoke(null, new object[] { value }) : value, null);
        }

        return copyInstance;
    }

I measured it in a simple way, by using the Watcher class.

 var person = new Person
 {
     ...
 };

 for (var i = 0; i < 1000000; i++)
 {
    personList.Add(person);
 }
 var watcher = new Stopwatch();
 watcher.Start();
 var copylist = personList.Select(CopyFactory.CreateCopyReflection).ToList();
 watcher.Stop();
 var elapsed = watcher.Elapsed;

RESULT: With inner object PersonInstance - 16.4, PersonInstance = null - 5.6

CopyFactory is just my test class where I have dozen of tests including usage of expression. You could implement this in another form in an extension or whatever. Don't forget about caching.

I didn't test serializing yet, but I doubt in an improvement with a million classes. I'll try something fast protobuf/newton.

P.S.: for the sake of reading simplicity, I only used auto-property here. I could update with FieldInfo, or you should easily implement this by your own.

I recently tested the Protocol Buffers serializer with the DeepClone function out of the box. It wins with 4.2 seconds on a million simple objects, but when it comes to inner objects, it wins with the result 7.4 seconds.

Serializer.DeepClone(personList);

SUMMARY: If you don't have access to the classes, then this will help. Otherwise it depends on the count of the objects. I think you could use reflection up to 10,000 objects (maybe a bit less), but for more than this the Protocol Buffers serializer will perform better.