C# 9.0: Record Types Non-Destructive Mutation (the With expression)

A C# 9.0 record type is immutable but there are times when it is useful to make a copy of a record type but only modify a subset of the properties. Under this scenario, the with express can be used with facilitates non-destructive mutation. To quote Steve Fenton's blog (C# 9 Non-Destructive Mutation): 

To demonstrate non-destructive mutation consider the following record type, a positional record (see C# 9.0: Positional Records):

public record Employee (
                  string Name, 
                  string Department,
                  string Office)
{
}    

The code below uses the with expression to make a copy of a record but allows specific properties to be changed in the newly created record and obviously does not modify the original record:

In the coding sample above, the first Employee record created is assigned to variable, victoria (line 13). The above code utilizes with expressions and behaves as follows:

• Line 14: the victoria record instance is used to create a new employee, mario, but assigns a new value to the Name property, Mario Aguayo,
• Line 15: the victoria record instance  is used to create a new employee, tarun, but assigns a new value to the Name property, Tarun Tiwari.
• Line 16: the victoria record instance  is used to create a new employee, kai, but assigns a new value to the Name property, Kai Feng and Department property, QA.
• Line 17: the kai record instance is used to create  a new employee, daisuke, but assigns a new value to the Name property, Daisuke Katchi and Office property, Via Carmen Suites.