Records in C# (Interview Guide) 

Records in C# are reference types (by default) designed for immutable data models with value-based equality.

They were introduced in C# 9 and improved in C# 10 & C# 11.

1. Why Records? (Interview Answer) 

Before Records, we used classes to store data:

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

Problem with Classes:

• Mutable (data can change)

• Reference equality (not value equality)

• More boilerplate code

Records solve this by:

• Immutable by default

• Value-based equality

• Less code

• Built-in ToString(), Equals(), GetHashCode()

2. Basic Record Example

public record Person(string Name, int Age);

Usage:

var person1 = new Person("John", 30);
var person2 = new Person("John", 30);

Console.WriteLine(person1 == person2); 

Output:

True

👉 Because Records compare values, not references.

3. Record vs Class (Important Interview Question) 

Class Example

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

var p1 = new Person { Name = "John", Age = 30 };
var p2 = new Person { Name = "John", Age = 30 };

Console.WriteLine(p1 == p2);

Output:

False

Record Example

public record Person(string Name, int Age);

var p1 = new Person("John", 30);
var p2 = new Person("John", 30);

Console.WriteLine(p1 == p2);

Output:

True

4. Immutability in Records 🔒

Records are immutable by default

public record Person(string Name, int Age);

var person = new Person("John", 30);

// person.Name = "David"; ❌ Error

5. "with" Keyword (Very Important Interview Question) 

Used to create a copy with modification

public record Person(string Name, int Age);

var person1 = new Person("John", 30);

var person2 = person1 with { Age = 35 };

Console.WriteLine(person1);
Console.WriteLine(person2);

Output:

Person { Name = John, Age = 30 }
Person { Name = John, Age = 35 }

👉 This is called Non-destructive mutation

6. Record with Properties

public record Person
{
    public string Name { get; init; }
    public int Age { get; init; }
}

Usage:

var person = new Person
{
    Name = "John",
    Age = 30
};

👉 init allows setting only during initialization

7. Record Inheritance

public record Person(string Name);

public record Employee(string Name, int Salary) : Person(Name);

Usage:

var emp = new Employee("John", 50000);
Console.WriteLine(emp);

8. Record Struct (C# 10) 

Records can also be structs

public record struct Person(string Name, int Age);

Difference:

Type	Memory
record	Reference Type
record struct	Value Type

9. Positional Records

public record Person(string Name, int Age);

Equivalent to:

public record Person
{
    public string Name { get; init; }
    public int Age { get; init; }
    
    public Person(string Name, int Age)
    {
        this.Name = Name;
        this.Age = Age;
    }
}

10. Deconstruction (Interview Favorite) 

public record Person(string Name, int Age);

var person = new Person("John", 30);

var (name, age) = person;

Console.WriteLine(name);
Console.WriteLine(age);

11. When to Use Records (Interview Answer) ✅

Use Records when:

✔ Data models
✔ DTOs
✔ Immutable objects
✔ Value comparison needed
✔ Read-only objects

Example:

public record EmployeeDto(int Id, string Name);

12. When NOT to Use Records ❌

Avoid Records when:

❌ Mutable objects needed
❌ Heavy business logic
❌ Entity Framework entities (sometimes not recommended)

13. Real-World Example (Interview Ready) 

public record Order(int Id, decimal Amount);

var order1 = new Order(1, 500);
var order2 = new Order(1, 500);

Console.WriteLine(order1 == order2);

Output:

True

14. Records vs Struct vs Class (Interview Table)

Feature	Class	Struct	Record
Type	Reference	Value	Reference
Immutable	No	No	Yes
Equality	Reference	Value	Value
Boilerplate	More	Less	Very Less
Use Case	Business Logic	Small Data	DTO/Data Models

15. Tricky Interview Questions 

Q1: Are Records immutable?

👉 Yes, by default (using init)

Q2: Are Records reference types?

👉 Yes (unless using record struct)

Q3: Can Records inherit?

👉 Yes

Q4: Can Records have methods?

👉 Yes

public record Person(string Name, int Age)
{
    public void Print()
    {
        Console.WriteLine(Name);
    }
}

Q5: Can we modify record values?

👉 Yes using with

var p2 = p1 with { Age = 40 };

16. Most Important Interview One-Liner 

Records are immutable reference types used for storing data with value-based equality.