immutable objects concept

[MAS-OUD]

On page 244, the concept of immutable objects is used. I think it would be a good idea to give a definition for this concept at the beginning of this section. The reader might not be aware of this already.

[markjprice]

Immutability is introduced on page 161. In the next edition, I will add a bit more text to this definition to make it clearer what it means. I should especially make it clear that records are not necessarily immutable! Thank you for raising this issue.

[markjprice]

I have added an item for this: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/improvements.md#page-161---using-lambdas-in-function-implementations