Shallow Copy and Deep Copy Using C#

Introduction

When we copy one instance to another using C# what happen is that both instances share the same memory address. But this is not the behavior we want most of the time.

When we create a copy of an object, for example:

MyClass obj=new MyClass()
MyClass obj2=obj;

Then the '=' operator copies the reference and not the object (and it works fine for a Value Type).

By default we get this behavior using the MemberwiseClone() method that is defined in the super class called System.Object. This is called “Shallow Copy”.

To get the same behavior for a Reference Type as well as a Value Type we use the Clone() method that belongs to the System.ICloneable interface. This is called a “Deep Copy”.

We will see both behaviors in depth one by one.

Shallow Copy

A Shallow Copy is about copying an object's value type fields into the target object and the object's reference types are copied as references into the target object but not the referenced object itself. It copies the types bit by bit. The result is that both instances are cloned and the original will refer to the same object.

We can get this behavior using MemberwiseClone() as mentioned earlier.

Now let's demonstrate this behavior using the following code:

class ShallowCopy
{
    public int I {get;set;}
    public int J {get;set;}
}

class Demo
{
    public static void Main()
    {
        ShallowCopy obj=new ShallowCopy();
        ShallowCopy objClone=obj;
        obj.I=10;// setting obj value after cloning..
        Console.WriteLine(“objvalue : {0} \t Clone value : {1}”,obj.I,objClone.I=10);
    }
}

Output : obj value : 10 Clone value : 10

Surprise! This is not what we were looking for, right? So here the MemberwiseClone() method is useful. Let's change the class as in the following:

class ShallowCopy :  ICloneable
{
    public int I {get;set;}
    public int J {get;set;}
    //method for cloning object
    public object Clone()
    {
        return this.MemberwiseClone();
    }
}
class Demo
{
    public static void Main()
    {
        ShallowCopy obj=new ShallowCopy();
        Console.WriteLine(“--------before Shellow Clopy------”);
        ShallowCopy objClone=obj;
        obj.I=10;// setting obj value after cloning..
        Console.WriteLine(“objvalue : {0} \t Clone value : {1}”,obj.I,objClone.I=10);
        Console.WriteLine(“--------after Shellow Copy------”);
        ShallowCopy objClone2=(ShallowCopy)obj.Clone();  // cast object to //ShallowCopy
        obj.I=1000;  // MemberwiseClone() will not use this reference..
        Console.WriteLine(“after using MemberwiseClone() Clone() method :{0}”,objClone2.I);
    }
}