Init-only setters in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of init-only property assignment

What will be the output of this C# code snippet using init-only setters?

C Sharp (C#)

public class Person {
    public string Name { get; init; }
}

var p = new Person { Name = "Alice" };
Console.WriteLine(p.Name);

A Alice

B null

C Compilation error

D Runtime exception

💡 Hint

Init-only properties can be set during object initialization.

The init-only setter allows setting the property only during object initialization. Here, Name is set to "Alice" when creating the object, so printing p.Name outputs "Alice".

❓ Predict Output

intermediate

Error when setting init-only property after initialization

What happens if you try to set an init-only property after the object is created?

C Sharp (C#)

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

var car = new Car { Model = "Sedan" };
car.Model = "Coupe";
Console.WriteLine(car.Model);

A Outputs "Sedan"

B Compilation error

C Outputs "Coupe"

D Runtime exception

💡 Hint

Init-only properties cannot be assigned outside initialization.

The line 'car.Model = "Coupe";' is invalid because init-only properties can only be set during initialization. This causes a compilation error.

🔧 Debug

advanced

Why does this init-only setter code fail to compile?

Identify the reason for the compilation error in this code using init-only setters.

C Sharp (C#)

public class Book {
    public string Title { get; init; }
}

var b = new Book();
b.Title = "C# Guide";
Console.WriteLine(b.Title);

A Title property must be readonly to use init-only

B Property Title is missing a setter

C Init-only property Title cannot be assigned outside object initialization

D Missing semicolon after object creation

💡 Hint

Check when init-only properties can be assigned.

Init-only properties can only be assigned during object initialization, not after. Here, 'b.Title = "C# Guide";' is outside initialization, causing a compile error.

🧠 Conceptual

advanced

Understanding init-only setters with inheritance

Given these classes, what is the output of the program?

C Sharp (C#)

public class Animal {
    public string Species { get; init; }
}

public class Dog : Animal {
    public string Breed { get; init; }
}

var dog = new Dog { Species = "Canine", Breed = "Beagle" };
Console.WriteLine($"{dog.Species} - {dog.Breed}");

A Canine - null

B Compilation error due to init-only in base class

C Runtime exception

D Canine - Beagle

💡 Hint

Init-only setters work with inheritance and can be set during initialization.

Both Species and Breed are init-only properties. They are set during object initialization, so the output is "Canine - Beagle".

📝 Syntax

expert

Which option causes a compilation error with init-only setters?

Which of the following code snippets will NOT compile due to incorrect use of init-only setters?

A var p = new Person { Name = "John" }; p.Name = "Jane";

B var p = new Person { Name = "John" }; Console.WriteLine(p.Name);

C Person p = new() { Name = "John" };

D var p = new Person(); var q = p with { Name = "Jane" };

💡 Hint

Remember when init-only properties can be assigned.

Option A tries to assign to the init-only property Name after initialization, causing a compilation error. Options A, C, and D are valid uses.