[jira] Commented: (PIG-1510) Add `deepCopy` for LogicalExpressions

["Daniel Dai (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PIG-1510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12890777#action_12890777 ] 

Daniel Dai commented on PIG-1510:
---------------------------------

Yes, this should be a useful functionality. It will be included in the next patch for PIG-1178. I will submit a patch very soon.

> Add `deepCopy` for LogicalExpressions
> -------------------------------------
>
>                 Key: PIG-1510
>                 URL: https://issues.apache.org/jira/browse/PIG-1510
>             Project: Pig
>          Issue Type: New Feature
>          Components: data
>    Affects Versions: 0.8.0
>            Reporter: Swati Jain
>            Assignee: Swati Jain
>             Fix For: 0.8.0
>
>
> It would be useful to have a way to `deepCopy` an expression. `deepCopy` will create a new object so that changes made to one object will not reflect in the copy. There are 2 reasons why we don't override clone.
> * It may be better to use `deepCopy` since the copy semantics are explicit (since deepCopy may be expensive).
> * A second important reason for defining `deepCopy` as a separate routine is that it can be passed a plan as an argument which will be updated as the expression is copied (through plan.add and plan.connect).
> The usage would look like the following:
> {noformat}
> LogicalExpressionPlan logicalPlan = new LogicalExpressionPlan();
> LogicalExpression copyExpression = origExpression.deepCopy( logicalPlan );
> {noformat}
> An immediate motivation for this would be for constructing the expressions that constitute the CNF form of an expression.

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