[GitHub] [incubator-druid] gianm commented on a change in pull request #8047: optimize single input column multi-value expressions

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

gianm commented on a change in pull request #8047: optimize single input column multi-value expressions
URL: https://github.com/apache/incubator-druid/pull/8047#discussion_r309002377
 
 

 ##########
 File path: core/src/main/java/org/apache/druid/math/expr/ApplyFunction.java
 ##########
 @@ -60,6 +60,17 @@
    */
   Set<Expr> getArrayInputs(List<Expr> args);
 
+  /**
+   * Returns true if apply function produces an array output
+   */
+  default boolean hasArrayOutput()
+  {
+    return false;
 
 Review comment:
   What if a function might sometimes return an array and might sometimes return a scalar? Is that:
   
   - Not allowed (functions should not differ in their return types in this way)
   - Allowed, and `hasArrayOutput` should be `true`
   - Allowed, and `hasArrayOutput` should be `false`
   
   Please adjust the javadocs appropriately.

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