[jboss-jira] [JBoss JIRA] (DROOLS-1422) Make AccumulateFunction simpler and more powerful
Geoffrey De Smet created DROOLS-1422:
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Summary: Make AccumulateFunction 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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