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().

Is there an easy way around this?

Answer 1

If you only care about value types...

And you know the type:

List<int> newList = new List<int>(oldList);

If you don't know the type before, you'll need a helper function:

List<T> Clone<T>(IEnumerable<T> oldList)
{
    return newList = new List<T>(oldList);
}

The just:

List<string> myNewList = Clone(myOldList);

Answer 2

You can use an extension method.

static class Extensions
{
    public static IList<T> Clone<T>(this IList<T> listToClone) where T: ICloneable
    {
        return listToClone.Select(item => (T)item.Clone()).ToList();
    }
}

Answer 3

If your elements are value types, then you can just do:

List<YourType> newList = new List<YourType>(oldList);

However, if they are reference types and you want a deep copy (assuming your elements properly implement ICloneable), you could do something like this:

List<ICloneable> oldList = new List<ICloneable>();
List<ICloneable> newList = new List<ICloneable>(oldList.Count);

oldList.ForEach((item) =>
    {
        newList.Add((ICloneable)item.Clone());
    });

Obviously, replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable.

If your element type doesn't support ICloneable but does have a copy-constructor, you could do this instead:

List<YourType> oldList = new List<YourType>();
List<YourType> newList = new List<YourType>(oldList.Count);

oldList.ForEach((item)=>
    {
        newList.Add(new YourType(item));
    });

Personally, I would avoid ICloneable because of the need to guarantee a deep copy of all members. Instead, I'd suggest the copy-constructor or a factory method like YourType.CopyFrom(YourType itemToCopy) that returns a new instance of YourType.

Any of these options could be wrapped by a method (extension or otherwise).

Answer 4

After a slight modification you can also clone:

public static T DeepClone<T>(T obj)
{
    T objResult;
    using (MemoryStream ms = new MemoryStream())
    {
        BinaryFormatter bf = new BinaryFormatter();
        bf.Serialize(ms, obj);
        ms.Position = 0;
        objResult = (T)bf.Deserialize(ms);
    }
    return objResult;
}

Answer 5

Use AutoMapper (or whatever mapping lib you prefer) to clone is simple and a lot maintainable.

Define your mapping:

Mapper.CreateMap<YourType, YourType>();

Do the magic:

YourTypeList.ConvertAll(Mapper.Map<YourType, YourType>);