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https://issues.apache.org/jira/browse/GROOVY-10074?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17340915#comment-17340915
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Eric Milles commented on GROOVY-10074:
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Suggestion from the mailing list of using Java's functional interfaces, like
{{Function}}, instead of {{Closure}} would be another way to go here.
> DGM: Fix transform generics for collect and similar
> ---------------------------------------------------
>
> Key: GROOVY-10074
> URL: https://issues.apache.org/jira/browse/GROOVY-10074
> Project: Groovy
> Issue Type: Improvement
> Components: groovy-jdk
> Reporter: Eric Milles
> Priority: Minor
>
> The {{collect}} DGM is defined like this for {{Iterable}}, arrays, etc.:
> {code:java}
> <T> List<T> collect(Object self, Closure<T> transform)
> <S,T> List<T> collect(S[] self, @ClosureParams(FirstParam.Component.class)
> Closure<T> transform)
> <S,T> List<T> collect(Iterable<S> self,
> @ClosureParams(FirstParam.FirstGenericType.class) Closure<T> transform)
> <S,T> List<T> collect(Iterator<S> self,
> @ClosureParams(FirstParam.FirstGenericType.class) Closure<T> transform)
> {code}
> and like this for the variants that accept an output collection:
> {code:java}
> <T> Collection<T> collect(Object self, Collection<T> collector, Closure<?
> extends T> transform)
> ...
> {code}
> I think {{Closure<? extends T>}} is better. It would allow plain {{collect}}
> to work for this example under STC without requiring {{? extends
> CharSequence}} on the target or a typecast for "it" or the call expression:
> {code:groovy}
> List<CharSequence> list = ['string'].collect { it }
> {code}
> For comparison, Java's {{Stream#map}} function is defined this way:
> {code:java}
> <R> Stream<R> map(Function<? super T, ? extends R> mapper)
> {code}
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