Shallow Copy and Deep Copy in C#

When we assign one object variable to another in several programming languages, such as Java or C#, we copy a reference to the object's location in memory, not the object itself. So, both variables point to the same object instance in memory. It contrasts value-type variables like ints, bools, etc., which directly contain the actual value.

For example:

Here, g1 and g2 are reference variables that store references (memory addresses) pointing to the actual MyClass object in memory, say address 5000. When we assign g1 to g2 with =, we are copying the reference, so now both g1 and g2 pointers refer to the SAME MyClass instance at address 5000.

Therefore, any changes made to the object via g1 or g2 will be visible when accessing the object through both because there is still only one actual object. It is different from copying a value type like an int, where g2 would store its independent copy of the value.

So, in summary, the = assignment operator with reference types copies the reference, not the actual object, causing both references to point to the same instance. Value types directly contain values, so the assignment copies the value into the new variable.

What is Shallow Copy?

A shallow copy of an object does not make new copies of the nested objects-rather, it copies the reference to the nested objects. It means the copied object points to the same nested objects as the original object.

In more detail:

• A new instance is created with exact copies of the values present in the original object when a shallow copy is made.
• References to lists, arrays, and other reference-type fields in the original object are copied to the new object. So, the new object points to the same nested objects.
• If the original object is modified, the nested objects are modified. Since the shallow copy points to the same nested objects, those changes would also be reflected in the copy.
• Essentially, the nested objects are "shared" between the original and shallow copied objects by reference instead of being copied. Only the top-level values are copied.

Example:

Let us take a C# program to show the Shallow copy concept.

Output:

Original: Person: Jane, Age: 25, Hobbies: Reading, Gaming, Traveling
Copy: Person: John, Age: 30, Hobbies: Reading, Gaming, Traveling

What is Deep Copy?

A deep copy is an object copy that fully duplicates all levels of nested objects in the original object. It means instead of copying object references to the nested objects, it creates new instances of those nested objects.

In more detail:

• When creating a deep copy, wholly new instances of nested objects are created recursively through all levels of nesting within the object.
• No object references are shared between the original and the deep-copied object. It isolates the copied object from any changes made to the original object after copying.
• Performing a deep copy requires additional processing/memory to create the duplicated nested objects, compared to a shallow copy. It enables true independence between the original and copied objects.
• Languages may provide built-in support for deep copying via copy constructors, clone methods, etc. Alternatively, a manual deep copy requires recursively traversing the object structure to create copies.

Example:

Let us take a C# program to show the Deep copy concept.

Output:

Original: Person: Virat, Age: 25
Copy: Person: Virat, Age: 30