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

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

There is a simple way to clone objects in C# using a JSON serializer and deserializer.

You can create an extension class:

using Newtonsoft.Json;

static class typeExtensions
{
    [Extension()]
    public static T jsonCloneObject<T>(T source)
    {
    string json = JsonConvert.SerializeObject(source);
    return JsonConvert.DeserializeObject<T>(json);
    }
}

To clone and object:

obj clonedObj = originalObj.jsonCloneObject;

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

To clone a list just call .ToList(). This creates a shallow copy.

Microsoft (R) Roslyn C# Compiler version 2.3.2.62116
Loading context from 'CSharpInteractive.rsp'.
Type "#help" for more information.
> var x = new List<int>() { 3, 4 };
> var y = x.ToList();
> x.Add(5)
> x
List<int>(3) { 3, 4, 5 }
> y
List<int>(2) { 3, 4 }
> 

Answer 5

Unless you need an actual clone of every single object inside your List<T>, the best way to clone a list is to create a new list with the old list as the collection parameter.

List<T> myList = ...;
List<T> cloneOfMyList = new List<T>(myList);

Changes to myList such as insert or remove will not affect cloneOfMyList and vice versa.

The actual objects the two Lists contain are still the same however.

Answer 6

If you need a cloned list with the same capacity, you can try this:

public static List<T> Clone<T>(this List<T> oldList)
{
    var newList = new List<T>(oldList.Capacity);
    newList.AddRange(oldList);
    return newList;
}