[rules-dev] BUG: [5.3.0.Final] CollectSetAccumulateFunction should probably use IdentityHashMap internally

[Mark Proctor]

There are two types of facts - stated and justified. As explained in the 
TMS section.

Justified facts are ALWAYS equality based, as it's the nature of TMS. 
The other part of engine for stated facts is customizable and may work 
in either equality mode or identity mode. Identity mode is default, as 
it's the most common way  java developers expect to work, knowledge 
based engineers may prefer eqality mode.

We do discuss this in the maual. If it's clear, then please do help beef 
up the docs on this. Fork the docs and submit a pull request, see:
http://www.athico.com/Getting_Involved/gettinginvolved.html

Mark
On 25/02/2012 19:41, SirMungus wrote:
> By the way, while checking into various scenarios prompted by Wolfgang's
> response, I came up with a very interesting test program:
>
> rule "Initialize"
>      salience 100
>      when
>          eval(true)
>      then
>          insert("one");
>          insert(new String("one"));
>          insertLogical("two");
>          insertLogical(new String("two"));
> end
>
> rule "Find strings"
>      salience 50
>      when
>          $s : String()
>      then
>          System.out.println("I found string: " + $s);
> end
>
> rule "Gather strings"
>      salience 50
>      when
>          accumulate(
>              $s : String(),
>              $sSet : collectSet( $s ),
>              $sList : collectList( $s ) )
>      then
>          System.out.println("Here is the set of all strings: " + $sSet);
>          System.out.println("Here is the list of all strings: " + $sList);
> end
>
> What would you expect that to output? How many "I found string: xxx" lines
> would there be? How many entries in the "set of all strings"? How many
> entries in the "list of all strings"?
>
> For my part, I figured there would be four "I found string: xxx" lines, two
> entries in the set, and four entries in the list.
>
> I was very surprised to find the following output:
>
> I found string: two
> I found string: one
> I found string: one
> Here is the set of all strings: [two, one]
> Here is the list of all strings: [one, one, two]
>
> This strongly suggests that "insert" objects are held in an
> identity-preserving structure, but that "insertLogical" objects are held in
> an equals()-based structure.
>
> I am glad for the identity-based handling of "insert" objects, especially
> considering that all of my inserted objects come from "outside" the engine.
> I would hate to see one of them fail to be considered by the rule engine.
>
> I can almost see some usefulness for the equals() behavior of insertLogical
> objects, but far more potential problems.
>
> I think it's slightly dangerous that these behaviors differ and that it is
> not, AFAIK, documented in a way that is clear to users of Drools.
>
> --
> View this message in context: http://drools.46999.n3.nabble.com/BUG-5-3-0-Final-CollectSetAccumulateFunction-should-probably-use-IdentityHashMap-internally-tp3774079p3775619.html
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