> On 18 Feb 2018, at 3:18 pm, Christopher Hunt <[email protected]> wrote:
>
> It just occurred to me that compound types might be the way to solve this eg
> `new Element with OOB[Span]`. I shall experiment further... and then PR the
> Akka stream doco with a section on OOB/instrumentation if there’s interest.
> I’m very interested to hear about what others think though.
On further reflection, I don’t think that compound types really help that much
given that it takes effort to deconstruct/reconstruct them through various
transformations (map etc.).
Also, I was wrong to name this topic in relation to “out of band data”. In
hindsight, I really meant element metadata. OOB is a separate signalling
mechanism.
I remain curious as to whether an Akka streams API along the lines of the
materialisation API has been considered for carrying additional data with an
element to avoid polluting code.
Here’s a bit of (untested) code illustrating my thinking by way of a solution:
Source
.single("hi")
.mapMetadataValue(_ => hiStartedEvent)
...
.viaMeta(hiEndedEvent)
…where `hiStartedEvent` starts/returns a OpenTracing Span and `hiEndedEvent`
takes a single arg of a Span and ends it.
Of course, it doesn’t have to be a Span carried through… it could be any
metadata you can imagine.
Thanks!
-C
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