1 files changed, 23 insertions, 0 deletions

diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatefulAggregator.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatefulAggregator.java
new file mode 100644
index 00000000..c215a511
--- /dev/null
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatefulAggregator.java
@@ -0,0 +1,23 @@
+package tools.refinery.store.query.term;
+
+import java.util.stream.Stream;
+
+public interface StatefulAggregator<R, T> extends Aggregator<R, T> {
+        StatefulAggregate<R, T> createEmptyAggregate();
+
+        @Override
+        default R aggregateStream(Stream<T> stream) {
+                var accumulator = createEmptyAggregate();
+                var iterator = stream.iterator();
+                while (iterator.hasNext()) {
+                        var value = iterator.next();
+                        accumulator.add(value);
+                }
+                return accumulator.getResult();
+        }
+
+        @Override
+        default R getEmptyResult() {
+                return createEmptyAggregate().getResult();
+        }
+}