With expressions for immutable copies in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a 'with expression' in C#?

A 'with expression' creates a new object by copying an existing immutable object and changing some of its properties without modifying the original.

beginner

How do 'with expressions' help with immutability?

They allow you to create modified copies of objects without changing the original, preserving immutability and avoiding side effects.

beginner

Given a record:

record Person(string Name, int Age);

How do you create a copy with a new Age using a with expression?

var olderPerson = person with { Age = person.Age + 1 };

This creates a new Person with the same Name but Age increased by 1.

intermediate

Can 'with expressions' be used with classes that are not records?

No, 'with expressions' work primarily with records or types that support them. Regular classes need custom cloning methods.

intermediate

What happens if you use a with expression but don't change any properties?

A new object is still created, but it has the same property values as the original, effectively a shallow copy.

What does the 'with' keyword do in C# records?

A Converts a record to a class

B Modifies the original record in place

C Deletes the record

D Creates a new record by copying and modifying specified properties

The 'with' keyword creates a new record by copying the original and changing specified properties.

Which of these is true about 'with expressions'?

A They create a new object with some changed properties

B They are used to delete properties

C They only work with mutable classes

D They mutate the original object

'With expressions' create a new object with some properties changed, leaving the original unchanged.

Given

record Point(int X, int Y);

How to create a new Point with X=5 but same Y as p?

A Both B and C

B var p2 = new Point(5, p.Y);

C var p2 = p with { X = 5 };

D None of the above

Both ways create a new Point with X=5 and Y same as p.Y.

Can you use 'with expressions' to change nested objects inside a record?

A Yes, directly and deeply

B No, only top-level properties can be changed

C Yes, but only if nested objects are mutable

D No, 'with' only works on classes

'With expressions' only create shallow copies and change top-level properties.

What C# feature introduced 'with expressions' for immutable copies?

A C# 7.0

B C# 8.0

C C# 9.0

D C# 10.0

'With expressions' were introduced in C# 9.0 along with records.

Explain how 'with expressions' help maintain immutability in C# records.

Think about how you can change data without changing the original object.

Describe the difference between using a 'with expression' and modifying an object directly.

Consider what happens to the original object in each case.