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https://issues.apache.org/jira/browse/TINKERPOP3-1013?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15034506#comment-15034506
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ASF GitHub Bot commented on TINKERPOP3-1013:
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GitHub user okram opened a pull request:
https://github.com/apache/incubator-tinkerpop/pull/165
TINKERPOP3-1013: Traverser tags as a safer way of using path labels
https://issues.apache.org/jira/browse/TINKERPOP3-1013
We have had a hack in `MatchStep` this whole time where we use path labels
to store branch history. This is not only semantically awkward (as labels are
added that were not provided via `as()`), it also means we will not be able to
do https://issues.apache.org/jira/browse/TINKERPOP3-736. Also, this will allow
us to cleanly implement `IntersectStep` and `SymetricDifferenceStep` (down the
road).
The implementation is really simple. `Traverser.getTags()`. This method
returns a mutable set and thus, we can remove, add, size, contains, etc. tags
associated with a traverser.
Ran `mvn clean install` and all is golden.
VOTE +1.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/apache/incubator-tinkerpop TINKERPOP3-1013
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-tinkerpop/pull/165.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #165
----
commit e6a1141a0515f8adc7e51adb2a84495349b06c6a
Author: Marko A. Rodriguez <[email protected]>
Date: 2015-12-01T20:16:26Z
Added Traverser.getTags(). This gives us more flexbility in how we handle
branch-history. This improves MatchStep, future IntersectStep, future
SymmetricDifferenceStep, and will allow us to do traversal rewriting in
MatchStep (TINKERPOP3-736). No more awkward hack of
traverser.path().extend(step.getId())... the stepID is NOT a path label, its a
tag.
----
> Traverser tags as a safer way of using path labels
> --------------------------------------------------
>
> Key: TINKERPOP3-1013
> URL: https://issues.apache.org/jira/browse/TINKERPOP3-1013
> Project: TinkerPop 3
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.1.0-incubating
> Reporter: Marko A. Rodriguez
> Assignee: Marko A. Rodriguez
> Fix For: 3.1.1-incubating
>
>
> We should add the following methods to {{Traverser}}.
> {code}
> void Traverser.addTag(final String tag)
> boolean Traverser.hasTag(final String tag)
> void Traverser.dropTag(final String tag)
> void Traverser.dropTags()
> {code}
> What is the point of a "tag" ? There are two use cases:
> 1. Currently {{MatchStep}} "tags" a traverser with
> {{traverser.getPath().addLabel(step.getId())}}. This means that the path
> data of the traverser is used to store which branches of the {{match()}} the
> traverser has already gone down. This is a hack as now the
> {{travesrer.path()}} has a weird step ID label. Also, its inefficient as the
> path needs to be searched for the respective "tag." A {{Set<String>}} is much
> more efficient.
> 2. Intersect/symmetric difference will require some sort of "tagging" as
> explained in Section 4 of http://arxiv.org/abs/1511.06278. We could, of
> course, use the {{MatchStep}} way of doing things, but again, thats a hack.
> 3. When we support TINKERPOP3-736, using the "{{path()}}-hack" will not work
> as two branches will have different stepIds but the same tag.
> In short, anytime we need to know if a particular branch of a traversal was
> taken, {{Traverser.getTag()}} is our friend.
> IMPORTANT: This will go into {{Traverser.Admin}} as no user should use these
> tags. These are simply for internal markup of traverser.
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