}
public BetaMemory createBetaMemory(final RuleBaseConfiguration config) {
BetaMemory memory;
if ( this.indexed ) {
final VariableConstraint variableConstraint = (VariableConstraint) this.constraint;
final FieldIndex index = new FieldIndex( variableConstraint.getFieldExtractor(),
variableConstraint.getRequiredDeclarations()[0],
variableConstraint.getEvaluator() );
LeftTupleMemory tupleMemory;
if ( this.conf.isIndexLeftBetaMemory() ) {
tupleMemory = new LeftTupleIndexHashTable( new FieldIndex[]{index} );
} else {
tupleMemory = new LeftTupleList();