Cloning independent instance

Question

The result of this code is "1" and "2". When i split Foo "a" it makes an instance "b" and everything what i do to "b", it happens to "a" too. Is there any solution to give back a compleatly independent instance of Foo? So the result of my code would be "1" and "1".

using System.IO;
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {

        Baar b0 = new Baar();
        Baar b1 = new Baar();
        Baar b2 = new Baar();
        Baar b3 = new Baar();
        Foo a = new Foo(200);
        a.addBaar(b0);

        Console.WriteLine(a.baars.Count);
        Foo b = a.split(100);

        b.addBaar(b1) ;      
        Console.WriteLine(a.baars.Count);

    }
}

class Foo
{
    public int amount;
    public List<Baar> baars = new List<Baar>();
    public Foo(int amount)
    {
        this.amount = amount;
    }

    private Foo(int amount, List<Baar> baars)
    {
        this.amount = amount;
        this.baars = baars;
    }

    public void addBaar(Baar baar)
    {
        this.baars.Add(baar);

    }

    public Foo split(int amount)
    {
        int diff = this.amount - amount;
        this.amount = amount;
        return new Foo(diff, this.baars);
    }
}

class Baar
{

    public Baar()
    {

    }
}

Answer 1

Your split method is passing around a reference to the same underlying baars list. This can be demonstrated simply with:

List<int> a = new List<int>();
a.Add(1);

Console.WriteLine(a.Count); //1

List<int> b = a;
b.Add(2);

Console.WriteLine(b.Count); //2
Console.WriteLine(a.Count); //2
Console.WriteLine(Object.ReferenceEquals(a, b)); //true

Instead, you want to pass a copy of that list:

public Foo split(int amount)
{
    int diff = this.amount - amount;
    this.amount = amount;
    List<Baar> baarsCopy = new List<Baar>(this.baars); //make a copy
    return new Foo(diff, baarsCopy); //pass the copy
}

EDIT: Beyond that, I don't know if you want to make copies of the Baar items inside that list as well or pass around/share references to the same Baar instances. That's up to you and your application usage.

Answer 2

Looks like you are talking about "deep cloning" objects. That question has been answered plenty of times already.

How do you do a deep copy of an object in .NET (C# specifically)?

Deep cloning objects