Deep copy of List<T> with extension method

Question

I have this class :

public class Person : ICloneable
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public object Clone()
    {
        return this;
    }
}

An extension method :

public static class MyHelper
{
    public static IEnumerable<T> Clone<T>(this IEnumerable<T> collection) where T : ICloneable
    {
        return collection.Select(item => (T)item.Clone());
    }
}

I'd like use it in this case :

var myList = new List<Person>{ 
    new Person { FirstName = "Dana", LastName = "Scully" },
    new Person{ FirstName = "Fox", LastName = "Mulder" }
};

List<Person> myCopy = myList.Clone().ToList<Person>();

When I change in the "immediat window" a value of myCopy , there is a change in the orginial list too.

I'd like have both list completely independent

I missed something ?

Answer 1

Your implementation of Clone is wrong.

Try this:

public object Clone()
{
    return MemberwiseClone();
}

Answer 2

Your clone method returns the same object.

You should implement it like this

public class Person : ICloneable
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public object Clone()
    {
        return new Person { FirstName = this.FirstName, LastName = this.LastName };
    }
}

Answer 3

Apart from the issue with your Clone method inside your Person class you need to return a new list in your extension method also

return collection.Select(item => (T)item.Clone()).ToList();

This is because the Select method is from Linq which uses deferred execution. If you change the original list then the list of 'myCopy' will also change.