C# 9.0 With-expressions. How to use them?

Question

The new C# 9.0 syntax allows for a new kind of expression:

var newPerson = oldPerson with { Age = "21" };

Following questions arise when looking at the previous code line:

1. Is it a reference or a new object copy?
2. If it's a reference, what about the inheritance? Consider the following code line:

Person child = new Child{ FirstName = "Jan", LastName = "Brown", IsInKindergarten = false };
Person person = child with { LastName = "Williams" }

Does the compiler allow the person object to inherit the IsInKindergarten property?

Answer 1

In this case var newPerson = oldPerson with { Age = "21" }; it creates a new object that’s a copy of the old one, except with a different age.

Does the compiler allow the person object to inherit the IsInKindergarten property?

yes, the person will be FirstName = "Jan", LastName = "Williams", IsInKindergarten = false

Answer 2

this syntax about record in c# 9.0 and this is Immutable type indeed all immutable types are creating new object like as struct for more information about this you can see this https://channel9.msdn.com/Shows/On-NET/C-9-Language-Features