[GitHub] incubator-metron issue #404: METRON-624: Updated Comparison/Equality Evaluat...

[cestella <gi...@git.apache.org>]

Github user cestella commented on the issue:

    https://github.com/apache/incubator-metron/pull/404
  
    Hey, thanks for the great addition @jjmeyer0!
    
    A few things to note and some context.
    
    Around validation, the initial stellar implementation purposefully ran validation the way that it's implemented, but we can reconsider those things if we want.
    * The variables resolve to `null` to ensure that functions could handle `null` without error.  I understand that Java and most programming languages would NPE on `1 < null`, but our data flowing through the topologies will be sparse, so not all variables will be defined for every message.  If a stellar statement is applied to a message where the variable is not defined, I wanted to ensure that it did not fail, but rather did an appropriate thing depending on the operation.
    * We do function resolution during validation to ensure people have not made a syntactic error in their stellar statements when pushing configs to zookeeper.  We would rather fail fast here.
    
    Around `==` for floating point numbers.  The initial stellar implementation intended to do an epsilon check on equals involving doubles (e.g. Math.abs(lhs - rhs) < epsilon) as you almost never want strict equality in floating point numbers.
    
    What this does show is that we need more of a rigorous spec and more time spent on documenting the design of Stellar.


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