Deep copy of List 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 ?

Why do you use the `ICloneable` interface? This interface is useless: http://stackoverflow.com/questions/536349/why-no-icloneablet. — Steven, Jul 31 '12 at 07:13

score 3 · Accepted Answer · answered Jul 31 '12 at 06:52

3

Your implementation of Clone is wrong.

Try this:

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

answered Jul 31 '12 at 06:52

leppie

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score 1 · Answer 2 · answered Jul 31 '12 at 06:50

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 };
    }
}

score 1 · Answer 3 · answered Jul 31 '12 at 06:54

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.

Deep copy of List with extension method

3 Answers3