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https://issues.apache.org/jira/browse/GROOVY-11486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King closed GROOVY-11486.
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> DGM flatten return type is often incorrect
> ------------------------------------------
>
> Key: GROOVY-11486
> URL: https://issues.apache.org/jira/browse/GROOVY-11486
> Project: Groovy
> Issue Type: Bug
> Reporter: Eric Milles
> Assignee: Eric Milles
> Priority: Major
> Fix For: 5.0.0-beta-1
>
>
> The groovy method {{flatten}} for {{Object[]}}, {{Collection}}, {{Iterable}},
> {{List}}, {{Set}} and {{SortedSet}} does not inference to the correct return
> type except for the case where there were no aggregate elements to flatten.
> There isn't anything the type checker can do to detect the return type for
> non-trivial cases, but the {{flatten}} methods that accept a transform are a
> reasonable model:
> {code:java}
> public static <T, E> Collection<T> flatten(Iterable<E> self, Closure<?>
> flattenUsing) {
> // ...
> }
> {code}
> This allows the programmer to declare the expected type:
> {code:groovy}
> def list = [1,[2],[[3],[4]]]
> Collection<Integer> coll = list.flatten(Closure.IDENTITY)
> {code}
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