Github user simonellistonball commented on the issue:
https://github.com/apache/metron/pull/1021
This is a great feature from my perspective. I've seen a number of people
try and build solutions that require access to the whole message for a bunch of
custom functions, models, rules engine integrations etc, and as a simple means
of doing this, I love the approach. To address some of the points here, I
agree, we need to avoid any chance of copying the whole map given the
performance risk with some potentially sizable and numerous objects.
Assignment... yep, _ should not be allowed on the left hand side, and it's a
map, so assignment to an output field shouldn't be a big issue.
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