With expressions for immutable copies in C Sharp (C#) - Step-by-Step Execution

Concept Flow - With expressions for immutable copies

Create original record

↓

Use 'with' expression

↓

Copy original with changes

↓

New record created, original unchanged

↓

Use new record as needed

Start with an original record, use 'with' to make a copy with some changes, resulting in a new record while the original stays the same.

Execution Sample

C Sharp (C#)

record Person(string Name, int Age);

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

Console.WriteLine(p1);
Console.WriteLine(p2);

Creates a Person record, then makes a copy with a changed Age using 'with' expression, printing both.

Execution Table

Step	Action	Variable Values	Output
1	Create p1 with Name='Alice', Age=30	p1 = Person(Name='Alice', Age=30)
2	Create p2 as copy of p1 with Age=31	p2 = Person(Name='Alice', Age=31)
3	Print p1	p1 unchanged	Person { Name = Alice, Age = 30 }
4	Print p2	p2 has Age=31	Person { Name = Alice, Age = 31 }
5	End	No changes

💡 Execution ends after printing both records; original remains unchanged.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
p1	undefined	Person(Name='Alice', Age=30)	Person(Name='Alice', Age=30)	Person(Name='Alice', Age=30)
p2	undefined	undefined	Person(Name='Alice', Age=31)	Person(Name='Alice', Age=31)

Key Moments - 2 Insights

Why does changing Age in p2 not affect p1?

Because 'with' creates a new copy with changes, leaving the original p1 unchanged, as shown in steps 2 and 3 of the execution_table.

Is p2 a reference to p1 or a new object?

p2 is a new object created by copying p1 and changing Age, not a reference to p1, as seen in variable_tracker after step 2.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the Age value of p2?

A 30

B undefined

C 31

D 0

💡 Hint

Check the 'Variable Values' column at step 2 in execution_table.

At which step does p1 get created?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for creation of p1.

If we changed p1's Name after step 1, would p2's Name change?

A No, because p2 is a copy made before the change

B Yes, because records are mutable

C Yes, because p2 references p1

D No, because p2 is unrelated

💡 Hint

Refer to variable_tracker and key_moments about immutability and copying.

Concept Snapshot

With expressions create a new immutable copy of a record with some changes.
Syntax: var newRecord = oldRecord with { Property = newValue };
Original record stays unchanged.
Useful for immutable data updates.
Works only with records or types supporting 'with'.

Full Transcript

This example shows how to use 'with' expressions in C# to create immutable copies of records. First, we create a record p1 with Name 'Alice' and Age 30. Then, using 'with', we create p2 as a copy of p1 but with Age changed to 31. Printing p1 and p2 shows that p1 remains unchanged while p2 has the updated Age. This demonstrates that 'with' expressions produce new objects without modifying the original, supporting safe immutable data handling.