Should structs always be immutable?

Question

I was reading a couple of threads on here about structs and there is/was one about structs and how they should be representing immutable values (eg like a digit - 1) because of their value type behaviour/semantics.

But on the other hand, structs represent things like phone numbers, which can change for the same household.

Is this a hard and fast rule?

Answer 1

A phone number does not change; you just get a different one and discard the old one. The old one is still the same it always was. Same with dates, numbers, etc. - think of this when approaching structs. They are a way to encapsulate a value - which simply is; not the usage of the value, which changes.