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https://issues.apache.org/jira/browse/COLLECTIONS-820?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Claude Warren updated COLLECTIONS-820:
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Summary: BloomFilter: support merge without checking (was: BloomFilter:
renaming merge/mergeInPlace)
> BloomFilter: support merge without checking
> -------------------------------------------
>
> Key: COLLECTIONS-820
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-820
> Project: Commons Collections
> Issue Type: Improvement
> Components: Collection
> Affects Versions: 4.5
> Reporter: Claude Warren
> Priority: Minor
> Labels: bloom-filter
>
> Support a merge without checking and then provide a method add with
> checking for a change in the filter. This will duplicate a lot of (simple)
> code. But it provides a nice method to check if a filter contains an object
> and do something if it did not, rather than calling contains before then
> doing a merge, or doing a merge and checking cardinality change afterwards.
> For a bitmap bloom filter this can be done branchless by accumulating all the
> zero bits that are set to 1 using:
> long[] flag = {0};
> int[] idx = new int[1];
> bitMapProducer.forEachBitMap(value -> {
> int i = idx[0]++;
> flag[0] |= (~bitMap[i] & value);
> bitMap[i] |= value;
> return true;
> });
> return flag[0] != 0;
> For a filter with an explicit cardinality you just check the cardinality
> before and after the merge.
> h3.
> !https://avatars.githubusercontent.com/u/886334?s=48&v=4|width=24,height=24!
> *[aherbert|https://github.com/aherbert]* [on 27
> Feb|https://github.com/apache/commons-collections/pull/258#discussion_r813419143]
>
> With the provision of the {{copy}} method the {{merge}} method seems
> redundant with {{{}mergeInPlace{}}}. It is equivalent to two lines of code:
>
> {{BloomFilter filter2 = filter.copy(); }}
> {{filter2.mergeInPlace(other);}}
>
> I think {{merge}} should be the collections equivalent of {{{}add{}}}. This
> acts in place. Very few collections operations return new collections unless
> they are views of the current collection, e.g. List.subList. Note that the
> CountingBloomFilter has {{add}} which acts in place. There is no {{add}}
> returning a new CountingBloomFilter and then an {{{}addInPlace{}}}. So there
> is some inconsistency here.
> IMO the more common operation is to merge a filter in place. So this should
> be the action of merge. Then the mergeInPlace can be dropped or replaced with
> {{copyAndMerge}} or {{{}mergeToCopy{}}}. You then also have the boolean
> result of merge to consider. Should the copy not be returned if the merge
> returns false? Since it is 2 lines of code I would not bother and drop this.
> The BloomFilter then has {{merge}} and CountingBloomFilter has {{{}add{}}},
> both act in place (the common operation). The user can create a copy if
> desired for a merge if that is useful to them.
> Another comment on {{merge}} suggests changing it to support {{add}} and
> {{merge}} as both have their own use cases.
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