stream
A SubscriptionRef[A] contains a RefM[A] and a Stream that will emit
every change to the RefM.
A Take[E, A] represents a single take from a queue modeling a stream of
values.
A Take[E, A] represents a single take from a queue modeling a stream of
values. A Take may be a failure cause Cause[E], an chunk value A
or an end-of-stream marker.
A ZStream[R, E, O] is a description of a program that, when evaluated,
may emit 0 or more values of type O, may fail with errors of type E
and uses an environment of type R.
A ZStream[R, E, O] is a description of a program that, when evaluated,
may emit 0 or more values of type O, may fail with errors of type E
and uses an environment of type R. One way to think of ZStream is as a
ZIO program that could emit multiple values.
Another analogue to ZStream is an imperative iterator:
trait Iterator[A] { def next: A }
This data type can emit multiple A values through multiple calls to next.
Similarly, embedded inside every ZStream is a ZIO program: ZIO[R, Option[E], Chunk[O]].
This program will be repeatedly evaluated as part of the stream execution. For
every evaluation, it will emit a chunk of values or end with an optional failure.
A failure of type None signals the end of the stream.
ZStream is a purely functional *pull* based stream. Pull based streams offer
inherent laziness and backpressure, relieving users of the need to manage buffers
between operators. As an optimization, ZStream does not emit single values, but
rather zio.Chunk values. This allows the cost of effect evaluation to be
amortized and most importantly, keeps primitives unboxed. This allows ZStream
to model network and file-based stream processing extremely efficiently.
The last important attribute of ZStream is resource management: it makes
heavy use of ZManaged to manage resources that are acquired
and released during the stream's lifetime.
ZStream forms a monad on its O type parameter, and has error management
facilities for its E type parameter, modeled similarly to ZIO (with some
adjustments for the multiple-valued nature of ZStream). These aspects allow
for rich and expressive composition of streams.
The current encoding of ZStream is *not* safe for recursion. ZStream programs
that are defined in terms of themselves will leak memory. For example, the following
implementation of ZStream#forever is not heap-safe:
def forever = self ++ foreverInstead, recursive operators must be defined explicitly. See the definition of ZStream#forever for an example. This limitation will be lifted in the future.
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