[GitHub] [incubator-doris] morrySnow commented on a diff in pull request #9807: [Enhancement](Nereids)rewrite framework used in Memo

[GitBox <gi...@apache.org>]

morrySnow commented on code in PR #9807:
URL: https://github.com/apache/incubator-doris/pull/9807#discussion_r885144758


##########
fe/fe-core/src/main/java/org/apache/doris/nereids/memo/GroupExpression.java:
##########
@@ -17,42 +17,47 @@
 
 package org.apache.doris.nereids.memo;
 
+import org.apache.doris.nereids.operators.Operator;
 import org.apache.doris.nereids.rules.Rule;
 import org.apache.doris.nereids.rules.RuleType;
-import org.apache.doris.nereids.trees.plans.Plan;
 
 import com.clearspring.analytics.util.Lists;
 
 import java.util.BitSet;
 import java.util.List;
+import java.util.Objects;
 
 /**
  * Representation for group expression in cascades optimizer.
  */
 public class GroupExpression {
     private Group parent;
     private List<Group> children;
-    private final Plan<?, ?> plan;
+    private final Operator op;
     private final BitSet ruleMasks;
     private boolean statDerived;
 
-    public GroupExpression(Plan<?, ?> plan) {
-        this(plan, Lists.newArrayList());
+    public GroupExpression(Operator op) {
+        this(op, Lists.newArrayList());
     }
 
     /**
      * Constructor for GroupExpression.
      *
-     * @param plan {@link Plan} to reference
+     * @param op {@link Operator} to reference
      * @param children children groups in memo
      */
-    public GroupExpression(Plan<?, ?> plan, List<Group> children) {
-        this.plan = plan;
-        this.children = children;
+    public GroupExpression(Operator op, List<Group> children) {
+        this.op = Objects.requireNonNull(op);
+        this.children = Objects.requireNonNull(children);
         this.ruleMasks = new BitSet(RuleType.SENTINEL.ordinal());
         this.statDerived = false;
     }
 
+    public int arity() {

Review Comment:
   In logic, mathematics, and computer science, the arity of a function or operation is the number of arguments or operands the function or operation accepts.



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