[jboss-jira] [JBoss JIRA] (DROOLS-1422) Make AccumulateFunction interface simpler and more powerful

[Geoffrey De Smet (JIRA)]

     [ https://issues.jboss.org/browse/DROOLS-1422?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Geoffrey De Smet updated DROOLS-1422:
-------------------------------------
    Summary: Make AccumulateFunction interface simpler and more powerful  (was: Make AccumulateFunction simpler and more powerful)


> Make AccumulateFunction interface simpler and more powerful
> -----------------------------------------------------------
>
>                 Key: DROOLS-1422
>                 URL: https://issues.jboss.org/browse/DROOLS-1422
>             Project: Drools
>          Issue Type: Feature Request
>          Components: core engine
>            Reporter: Geoffrey De Smet
>            Assignee: Mario Fusco
>
> * Replace the AccumulateFunction interface with the AccumulateFunction2 interface:
> ** All core runtime code uses the AccumulateFunction2 interface.
> **  Deprecate AccumulateFunction and use a bridge class at DRL compilation time so old implementations still work because they are bridged into the new interface
> * Changes of the AccumulateFunction2:
> ** Methods no longer throw checked exceptions (no "throws Exception"), so drools doesn't have to catch them. This might improve performance.
> ** Remove "Serializable context". The class itself contains the state.
> *** Remove method createContext()
> *** Replace method init(Serializeble) with constructor call (no-args normally)
> *** Remove parameter Serializable from accumulate(value), reserve(value) and getResult() methods
> *** This might improve performance.
> ** It should Serializable, but doesn't have to Externalizable. Removes methods writeExternal() and readExternal() in the user implementation.
> * Interface ReversableAccumulateFunction2 extends AccumulateFunction2
> ** Only ReversableAccumulateFunction2 has method reverse(value)
> ** Remove method supportsReverse(): the custom accumulate is reverseable if it also implements this interface
> * Opportunities
> ** construction parameters. For example: fixed average for standard deviation (very useful for OptaPlanner)
> ** Multi-argument accumulates, for example in DRL: `$total : standardDeviation($groupBy, $weight)`
> {code}
> public class SumAccumulateFunction
>         implements ReversableAccumulateFunction2<Integer, Integer> {
>     public int total;
>     public SumAccumulateFunction() {
>         total = 0;
>     }
>     public void accumulate(Integer value) {
>         total += value;
>     }
>     public void reverse(Integer value) {
>         total -= value;
>     }
>     public Integer getResult() {
>         return total;
>     }
> }
> {code}
> {code}
> public class AverageAccumulateFunction
>         implements ReversableAccumulateFunction2<Integer, Double> {
>     public int total;
>     public int count;
>     public AverageAccumulateFunction() {
>         total = 0;
>         count = 0;
>     }
>     public void accumulate(Integer value) {
>         total += value;
>         count++;
>     }
>     public void reverse(Integer value) {
>         total -= value;
>         count--;
>     }
>     public Double getResult() {
>         return (double) total / count;
>     }
> }
> {code}
> {code}
> public class StdDeviationAccumulateFunction
>         implements ReversableAccumulateFunction2<Integer, Double> {
>     public final double average;
>     public double variance;
>     public StdDeviationAccumulateFunction(double average) {
>         this.average = average;
>         variance = 0;
>     }
>     public void accumulate(double value) {
>         variance += (value - average)²; // TODO
>     }
>     public void reverse(double value) {
>         variance -= (value - average)²; // TODO
>     }
>     public Double getResult() {
>         return Math.sqrt(variance);
>     }
> }
> {code}



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