With expressions for immutable copies in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple with expression on a record

What is the output of this C# code using a with expression on a record?

C Sharp (C#)

public record Person(string Name, int Age);

var p1 = new Person("Alice", 30);
var p2 = p1 with { Age = 31 };

System.Console.WriteLine(p2);

A Person { Name = Alice, Age = 31 }

B Person { Name = Alice, Age = 30 }

C Person { Name = , Age = 31 }

D Compilation error

💡 Hint

The with expression creates a new record copying all properties except those changed.

The with expression creates a new Person record copying all properties from p1 but sets Age to 31. So the output shows the updated Age.

❓ Predict Output

intermediate

Effect of with expression on nested records

Given these nested records, what is the output of the code below?

C Sharp (C#)

public record Address(string City, string Country);
public record Employee(string Name, Address Address);

var e1 = new Employee("Bob", new Address("Paris", "France"));
var e2 = e1 with { Address = e1.Address with { City = "Lyon" } };

System.Console.WriteLine(e2.Address.City);

A Compilation error

B Paris

C France

D Lyon

💡 Hint

With expressions can be nested to create copies with changes in nested properties.

The code creates a new Employee e2 with a new Address where City is changed to Lyon. So printing e2.Address.City outputs Lyon.

❓ Predict Output

advanced

Output when using with expression on a class instead of a record

What happens when you try to use a with expression on a class instead of a record in C#?

C Sharp (C#)

public class Car { public string Model { get; init; } public int Year { get; init; } }

var c1 = new Car { Model = "Tesla", Year = 2020 };
var c2 = c1 with { Year = 2021 };

System.Console.WriteLine(c2.Year);

A Compilation error

B 2020

C 2021

D Runtime error

💡 Hint

With expressions only work on records by default.

With expressions are supported only on records. Using them on classes causes a compilation error.

❓ Predict Output

advanced

Output of with expression with positional record and property change

What is the output of this code using a positional record and a with expression changing a property?

C Sharp (C#)

public record Point(int X, int Y);

var p1 = new Point(5, 10);
var p2 = p1 with { Y = 20 };

System.Console.WriteLine($"X={p2.X}, Y={p2.Y}");

A X=5, Y=10

B X=5, Y=20

C X=0, Y=20

D Compilation error

💡 Hint

With expressions copy all properties except those changed.

The with expression creates a new Point with X copied as 5 and Y changed to 20.

❓ Predict Output

expert

Output of with expression with inheritance and init-only properties

Consider these records with inheritance. What is the output of the code below?

C Sharp (C#)

public record Animal(string Name);
public record Dog(string Name, string Breed) : Animal(Name);

var d1 = new Dog("Buddy", "Beagle");
var d2 = d1 with { Breed = "Labrador" };

System.Console.WriteLine($"Name: {d2.Name}, Breed: {d2.Breed}");

A Name: Buddy, Breed: Beagle

B Name: , Breed: Labrador

C Name: Buddy, Breed: Labrador

D Compilation error

💡 Hint

With expressions work with inheritance and copy base properties automatically.

The with expression creates a new Dog copying Name from d1 and changing Breed to Labrador.