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https://issues.apache.org/jira/browse/GROOVY-8537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16429826#comment-16429826
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Venkatesh-Prasad Ranganath commented on GROOVY-8537:
----------------------------------------------------
A PR to fix this issue has been submitted –
https://github.com/apache/groovy/pull/682.
> GroovyCollections.combinations(Iterable) exhibits incorrect (asymmetric)
> behavior
> ---------------------------------------------------------------------------------
>
> Key: GROOVY-8537
> URL: https://issues.apache.org/jira/browse/GROOVY-8537
> Project: Groovy
> Issue Type: Bug
> Components: groovy-jdk
> Affects Versions: 2.4.15
> Reporter: Venkatesh-Prasad Ranganath
> Priority: Major
> Labels: easyfix
>
> h4. *Issue*
> When GroovyCollections.combinations() is invoked on a collection of iterables
> with at least one empty iterable, the expected return value is an empty list
> of combinations.
> Instead, in version 2.4.15 (and I am guessing in earlier versions at least
> since 2.2.0), the return value of combinations() is sensitive to the order of
> iterables in the input collection. Here are two instances of such behavior.
> h4. Repro
> {{groovy:000> assert [[1,3], []].combinations() == [[],
> [1,3]].combinations()}}
> {{ERROR org.codehaus.groovy.runtime.powerassert.PowerAssertionError:}}
> {{assert [[1,3], []].combinations() == [[], [1,3]].combinations()}}
> {{ | | |}}
> {{ [] false [[1], [3]]}}
>
> {{groovy:000> assert [[1,3], [2], []].combinations() == [[1,3], [],
> [2]].combinations()}}
> {{ERROR org.codehaus.groovy.runtime.powerassert.PowerAssertionError:}}
> {{assert [[1,3], [2], []].combinations() == [[1,3], [], [2]].combinations()}}
> {{ | | |}}
> {{ [] false [[2]]}}
> h4. *Fix*
> Add a short-circuiting check at the start of combinations(Iterable) method to
> return an empty list of combination if any of the input iterables are empty.
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