A type class for the building of efficient compact Immutable Arrays. Instances for this type class for classes / traits you control should go in the companion object of B not the companion object of BB. This is different from the related ArrBinder[BB] type class where instance should go into the BB companion object. The type parameter is named B rather than A, because normally this will be found by an implicit in the context of a function from A => B or A => M[B]. The methods of this trait mutate and therefore must be used with care. Where ever possible they should not be used directly by end users.