[
https://issues.apache.org/jira/browse/PIG-1510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12899282#action_12899282
]
Swati Jain commented on PIG-1510:
---------------------------------
We make a copy of all instance variables, including fieldSchema variables in
expression classes. Exceptions are:
a) Object val in ConstantExpression. We just copy a reference to the constant
object value since the object is constant by definition.
b) `fieldSchema` and `uidOnlyFieldSchema` in LogicalExpression.java since these
can be constructed when required from the expression copy by invoking
`getFieldSchema` and don't need to be copied.
> 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
>
> Attachments: deepCopy.patch, deepCopy.patch
>
>
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
