Understanding Deep Copy and Shallow Copy in Programming

When you work with objects in programming, sometimes you need to make a copy of an object. But do you know there are two types of copying? They are called shallow copy and deep copy. Understanding the difference is very important, especially in object-oriented programming.

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What is a Shallow Copy?

A shallow copy means copying the object’s top-level properties, but not the nested objects inside. If the original object has properties that are themselves objects, the shallow copy will only copy the reference (or address) of those inner objects.

This means:

• The copied object and the original object share the same nested objects.
• If you change a nested object through the copy, the original object will also see this change.

Example:

Imagine you have a box (object) that holds a small box (nested object) inside. Shallow copy copies the big box but both boxes share the same small box inside.

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What is a Deep Copy?

A deep copy means copying the object and all objects inside it, recursively. So every nested object is also copied, not shared.

This means:

• The copied object and the original object are completely independent.
• Changing any part of the copy will not affect the original object at all.

Example:

Using the box example again, deep copy means you copy the big box and also copy the small box inside it. Now the two big boxes do not share any parts.

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Why Does It Matter?

When you copy objects without knowing the difference, you can get unexpected bugs.

For example, if you do a shallow copy and then change the nested data in the copy, the original object will also change. This can cause problems if you want the original object to stay the same.

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When to Use Shallow Copy?

• When your object only has simple data types like numbers, strings, or booleans.
• When you want better performance because shallow copy is faster.
• When it is okay for the original and copied objects to share nested objects.

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When to Use Deep Copy?

• When your object contains other objects (nested objects).
• When you want to make sure the original object does not change after copying.
• When you want the copy to be completely independent.

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Summary Table

Feature	Shallow Copy	Deep Copy
Copies nested objects?	No, only copies references	Yes, copies all nested objects
Independence	Shared nested objects	Fully independent copies
Performance	Faster	Slower, more memory used
Use case	Simple objects, performance needed	Complex objects, data safety needed