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https://issues.apache.org/jira/browse/OAK-1110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13802905#comment-13802905
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Jukka Zitting commented on OAK-1110:
------------------------------------
This goes a bit against the original design idea behind the {{NodeStateDiff}}
mechanism, i.e. that the decision on whether to recurse down a subtree is done
*inside* a method like {{childNodeChanged()}}.
As for the {{MoveAwareNodeStateDiff}}, I think that also bends the
{{NodeStateDiff}} design in troublesome ways. So far the diff mechanism is
explicitly path-independent, and any path tracking is expected to happen inside
the diff implementations instead of the by the caller. The {{move}} method
breaks that pattern.
What would IMHO be a better solution here is an interface that's more like
{{Validator}} or {{Editor}} (that were explicitly designed to be composable)
where the recursion is explicitly done by the caller. Or possibly using the
Strategy pattern inside the diff implementation to make the relevant-or-not and
recurse-or-not decisions pluggable.
> Make NodeStateDiff composable
> -----------------------------
>
> Key: OAK-1110
> URL: https://issues.apache.org/jira/browse/OAK-1110
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core
> Reporter: Michael Dürig
> Attachments: OAK-1110.patch
>
>
> Currently it is not possible to warp a {{NodeStateDiff}} instance into
> another one for delegation. The problem is that recursion is done by the
> consumer of the {{childNodeChanged()}} call back which causes wrapped
> {{NodeStateDiff}} "to escape". To fix that I propose to separate the concerns
> of change notification from recursing into a subtree. For this we need an
> extra method {{createChildDiff}} on the {{NodeStateDiff}} interface:
> {code}
> /**
> * Create a {@code NodeStateDiff} for diffing the passed {@code before}
> and
> * {@code after} states. Returning {@code null} skips comparison for the
> sub
> * trees rooted at the passed states.
> *
> * @param name name of the child node
> * @param before before state of the child node
> * @param after after state of the child node
> * @return {@code NodeStateDiff} for the child node
> */
> @CheckForNull
> NodeStateDiff createChildDiff(String name, NodeState before, NodeState
> after);
> {code}
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