# package:copilot-language

Create a stream that carries a field of a struct in another stream. This function implements a projection of a field of a struct over time. For example, if a struct of type T has two fields, t1 of type Int and t2 of type Word8, and s is a stream of type Stream T, then s # t2 has type Stream Word8 and contains the values of the t2 field of the structs in s at any point in time.

Pair a stream with a field accessor, without applying it to obtain the value of the field. This function is needed to refer to a field accessor when the goal is to update the field value, not just to read it.