[GitHub] [calcite] danny0405 commented on a change in pull request #1276: [CALCITE-3137] AssertionError when reconstructing STRUCTURED type fields

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danny0405 commented on a change in pull request #1276: [CALCITE-3137] AssertionError when reconstructing STRUCTURED type fields
URL: https://github.com/apache/calcite/pull/1276#discussion_r303434966
 
 

 ##########
 File path: core/src/main/java/org/apache/calcite/sql/fun/SqlNewOperator.java
 ##########
 @@ -49,6 +50,14 @@ public SqlNode rewriteCall(SqlValidator validator, SqlCall call) {
   public boolean requiresDecimalExpansion() {
     return false;
   }
+
+  @Override public boolean validRexOperands(int count, Litmus litmus) {
+    if (count <= 0) {
+      return litmus.fail("wrong operand count {} for {}, Need at least one RexOperand!",
+          count, this);
+    }
+    return litmus.succeed();
+  }
 
 Review comment:
   Here is the java doc of `SqlNewOperator`:
   >SqlNewOperator represents an SQL <code>new specification</code> such as
   <code>NEW UDT(1, 2)</code>. When used in an SqlCall, SqlNewOperator takes a
   single operand, which is an invocation of the constructor method; but when
   used in a RexCall, the operands are the initial values to be used for the new
   instance.
   
   The `validRexOperands` method is only invoked in `RexCall` constructor, so i think overriding is the right way to go. But why we must require the count bigger than 0, how about there is a user defined constructor without any operands ? 

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