I don't think it is. Effective Go says that Go doesn't provide automatic support for getters and setters but there's nothing wrong with providing them yourself. Since in that case they are actually doing something (checking/updating the bitfield that contains the presence of each field), it makes sense to use them.

They are called `GetFoo()` instead of the idiomatic `Foo()`, but that is to ensure compatibility with the API where the fields are directly exposed as `Foo`, which also makes sense.