KIP-365: Make KStream.process processorSupplier parameter call by name

[joan38]

def process(processorSupplier: () => Processor[K, V], stateStoreNames: String*)

should be:

def process(processorSupplier: => Processor[K, V], stateStoreNames: String*)

KIP: https://cwiki.apache.org/confluence/pages/resumedraft.action?draftId=89069981&draftShareId=a21bcef4-c388-4663-9c6f-9ccceee4cb30

[joan38]

Just realised that by name parameters are evaluated only once.
Which invalidates this change.

[vvcephei]

@joan38 By-name parameters are evaluated every time they are dereferenced. But we did actually previously discuss a change like this, and decided against it.

The main reason is that this would be ok:

myThing.process(new Processor()...)

but this is a bug:

val processor = new Processor()...
myThing.process(processor)

which is just waaay to subtle.

[vvcephei]

requiring a 0-arity function makes it much clearer that we need the ability to generate fresh Processors at will.

[vvcephei]

But just to reiterate, we really appreciate your work in polishing this API. Thanks again!

[joan38]

https://docs.scala-lang.org/tour/by-name-parameters.html

by-value parameters have the advantage that they are evaluated only once

Anyway I went through exactly all what you explained in my head after opening the PR.

Thanks mate, I actually enjoy contributing here :)
I'm based in London right now but got a job in San Francisco, if my visa application goes through I'll be moving there.
In any case I'd be happy to meet other contributors to Kafka around a beer or 2. Just ping me!

[vvcephei]

For sure! Myself, I'm in Austin, but I head out there a few times a year. Just let us know!

[vvcephei]

oh, that doc says "by-value parameters", I thought we were talking about by-name parameters.

[joan38]

Indeed I read it wrong xD