Understanding Mutability and Immutability in C#


The terms "mutable" and "immutable" refer to object properties that can be modified after they are created in object-oriented programming. Understanding these concepts is crucial in writing robust and maintainable code in C#.

Mutability in C#

An object that can be modified after creation is said to be mutable. Let's consider a class representing a person with mutable properties.

public class MutablePerson
    public string Name { get; set; }
    public int Age { get; set; }

Let's create an instance of this class and modify its properties.

MutablePerson person = new MutablePerson { Name = "Mike", Age = 35 };

// Modifying the state of the object
person. Name = "Lisa";
person. Age = 30;

The flexibility of mutable objects comes with challenges related to data integrity and thread safety.

Immutability in C#

As opposed to mutable objects, immutable objects can't be modified once they're created. This simplifies code and enhances predictability.

public class ImmutablePerson
    public string Name { get; }
    public int Age { get; }

    public ImmutablePerson(string name, int age)
        Name = name;
        Age = age;

Let's use the immutable class now.

ImmutablePerson person = new ImmutablePerson("Mike", 35);

// Attempting to modify the state will result in a compilation error
// person. Name = "Lisa"; // Compilation error
// person.Age = 30; // Compilation error

Benefits of Immutability

  • Thread Safety: Immutable objects are thread-safe by definition since their state cannot be altered.
  • Predictability: Since the state remains constant, you can trust that the object will not change unexpectedly.
  • Debugging: The state of an immutable object is constant, making debugging easier.
  • Functional Programming: Immutability aligns well with functional programming principles, making code more reliable and predictable.


The choice between mutability and immutability depends on the requirements of your application and what benefits you wish to achieve. Mutability offers flexibility, while immutability ensures safety and predictability. Immutability is ideal for scenarios where predictability, thread safety, and simplicity are essential.

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