GitHub user ottobackwards opened a pull request:

    https://github.com/apache/metron/pull/687

    METRON-1090 [NO MERGE UNTIL METRON-711] Add Assignment to Stellar Language

    This PR adds support for Assignment to the Stellar Language.  It is 
dependent on [METRON-711](https://github.com/apache/metron/pull/686) before it 
can be merge.
    
    I still need to do the doc work, and more testing.
    
    ## Concept
    
    - Allow for assignment of values to variables only
    - Assignment both returns the assigned value AND updates the variable
    - VariableResolver implementation may or may not choose to support updates
    - The Shell handles all assignments ( foo := 'val' ) as ("foo = 'val'"). 
Exposing the whole operation to Stellar allows catching illegal values and 
grammar
    - The LambdaExpression does attempt to update variables, but this would 
have effect if the state was using a VariableResolver instance that supported 
updates AND the variable was not a 'lambda' variable.
    
    ```java
     String expr  = "MAP([ foo, bar, baz ], (item) -> count *= 2  )";
          Map<String,Object> map = new HashMap<String,Object>(){{
            put("foo",1);
            put("bar",1);
            put("baz",1);
            put("count", 1);
          }};
          for(int i = 0 ; i < 5; i++){
            run(expr, map);
          }
          Assert.assertEquals(new DecimalFormat("#").format(Math.pow(2,15)), 
map.get("count").toString());
    ```
    
    Support for:
    = , +=, -=, *=,  /=
    
    
    ## Side effects:
    This is opt-in for the resolvers.  The MapVariableResolver does NOT support 
update, so there is no change to Enrichment, Parsers, Profile, and Shell ( 
beyond what has been mentioned ). 
    
    ## Testing:
    See BasicStellarTest:test*Assign() for some usages.
    
    - Existing profiles, enrichments, parser transforms would work
    - Run different statements in the shell ( including those that would have 
worked before like = := 6.
     - more to come
    
    
    > This PR is to get the concept as a proposal out for review and start the 
discussion.  I will start a 
    > discuss thread as well.
    ---------
    > Note: This PR resolves [METRON-693 : Stellar REPL lets reserved tokens be 
used as unusable variable 
names](https://issues.apache.org/jira/browse/METRON-693)  as well.
    
    
    ## Pull Request Checklist
    
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    - [x] Is there a JIRA ticket associated with this PR? If not one needs to 
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    > and METRON-711
    
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You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/ottobackwards/metron stellar_assign

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/metron/pull/687.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #687
    
----
commit 215dc969026fa557a0a0f3efb9fe2bc170666b9a
Author: Otto Fowler <ottobackwa...@gmail.com>
Date:   2017-08-06T02:14:51Z

    Do not set variables when exceptions are thrown from assignment.
    Also remove executeStellar which is not required, if it doesn't eat the 
exception

commit f8e2fa9bdecd48fd70f03f2337439582ce341e21
Author: Otto Fowler <ottobackwa...@gmail.com>
Date:   2017-08-06T14:20:32Z

    Adds Variable Assignment to the Stellar Lanaguage
    
    =, +=, -=, *=, /=
    
    This are valid for assignment to variables.  All assignments return the 
value assigned,
    as other scripting languages do.
    
    VariableResolver extended with an update() method, though it may not be 
supported
    by all resolvers, this gives the ability to update variables and save 
between calls.
    
    The shell was updated for this, such that assignment calls
    
    More testing need and doc but I wanted to get it out there.
    This is dependent on PR 686

----


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