Mutating immutable obects: with=

[AlwaysHC]

public record Person(string FistName, string LastName);

Person person = new Person("John", "Doe");

//Changing last name...
person = person with { LastName = "Smith" };
//Proposal...
person with= { LastName = "Smith" };

[siegfriedpammer]

The proposed syntax looks awful in my opinion. Also I don't think this feature is worth the effort.

[333fred]

Very similar to #8114.

[DavidArno]

For me, the syntax isn't the issue, it's the idea that making it easy to replace an existing reference to a read-only thing with a reference to a new read-only thing is desirable. This feels like an attempt to work around the fact that record classes are read-only, rather than adding anything useful to the language.

x = x with { P = newValue } feels like a code smell to me. Either it's a new thing, so assign it to a new variable,
y = x with { P = newValue } or don't use a record class and allow the properties to be writable, x.P = newValue.