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https://issues.apache.org/jira/browse/CALCITE-2657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16677891#comment-16677891
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Julian Hyde commented on CALCITE-2657:
--------------------------------------
Note the comment in RexCall:
{code}
* <p>It's not often necessary to sub-class this class. The smarts should be in
* the operator, rather than the call. Any extra information about the call can
* often be encoded as extra arguments. (These don't need to be hidden, because
* no one is going to be generating source code from this tree.)</p>
{code}
So, we don't want to encourage sub-classing. Of the sub-classes that do exist,
two of them - RexOver and RexSubQuery - have specific handler methods in
RexShuttle. Adding handler methods is not something we would allow for code
outside of Calcite.
> use RexCall#clone instead of constructor to make a new RexCall in RexShuttle
> for more scalability
> -------------------------------------------------------------------------------------------------
>
> Key: CALCITE-2657
> URL: https://issues.apache.org/jira/browse/CALCITE-2657
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.17.0
> Reporter: Chunwei Lei
> Assignee: Julian Hyde
> Priority: Major
> Fix For: 1.18.0
>
>
> RexShuttle uses constructor of RexCall to generate a new RexCall, as
> followings:
> {code:java}
> public RexNode visitCall(final RexCall call) {
> boolean[] update = {false};
> List<RexNode> clonedOperands = visitList(call.operands, update);
> if (update[0]) {
> // REVIEW jvs 8-Mar-2005: This doesn't take into account
> // the fact that a rewrite may have changed the result type.
> // To do that, we would need to take a RexBuilder and
> // watch out for special operators like CAST and NEW where
> // the type is embedded in the original call.
> return new RexCall(
> call.getType(),
> call.getOperator(),
> clonedOperands);
> } else {
> return call;
> }
> }
> {code}
> It is more scalability when using RexCall#clone() for those using sub-class
> of RexCall since function clone can be override by sub-class, as followings:
> {code:java}
> public RexNode visitCall(final RexCall call) {
> boolean[] update = {false};
> List<RexNode> clonedOperands = visitList(call.operands, update);
> if (update[0]) {
> // REVIEW jvs 8-Mar-2005: This doesn't take into account
> // the fact that a rewrite may have changed the result type.
> // To do that, we would need to take a RexBuilder and
> // watch out for special operators like CAST and NEW where
> // the type is embedded in the original call.
> return call.clone(call.getType(), clonedOperands);
> } else {
> return call;
> }
> }
> {code}
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