ZIO Streams: Which is the difference between a ZSink and a ZTransducer?

Question

I'm studying ZIO Streams, using version 1.0.9 of the library zio-streams. I cannot find any reference that shows me the difference between a ZSink and a ZTransducer.

What is the difference?

Answer 1

A ZSink is a used to consume elements from the ZStream. In turn a sink will cause the materialization of the entire stream to run through and produce a value.

A ZTransducer is a stateful function which processes chunks of data in the stream, and in contrast to a ZSink it's processing never ends.

If we look at a trivial example:

import zio.stream.{ ZSink, ZStream }
import zio.stream.ZTransducer.{ splitLines, utf8Decode }

import java.nio.file.Paths

ZStream
  .fromFile(Paths.get("/foo"), chunkSize = 1024 * 4)
  .transduce(utf8Decode >>> splitLines)
  .run(ZSink.foreach(zio.console.putStr))

We can see that the new ZStream encoding is chunk based, and using transduce with utf8Decode which decodes a chunk of bytes to String and then splits them by line. Finally, we use the .run method and supply a ZSink which emits data to the console, element by element.

More on the new design of ZStream can be found here.