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https://issues.apache.org/jira/browse/FLINK-3681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Till Rohrmann closed FLINK-3681.
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Resolution: Fixed
Fixed via 833339f3a0faafbab9af90433488393421ae7171
> CEP library does not support Java 8 lambdas as select function
> --------------------------------------------------------------
>
> Key: FLINK-3681
> URL: https://issues.apache.org/jira/browse/FLINK-3681
> Project: Flink
> Issue Type: Bug
> Components: CEP
> Affects Versions: 1.0.0
> Reporter: Till Rohrmann
> Assignee: Till Rohrmann
> Priority: Minor
> Fix For: 1.1.0, 1.0.1
>
>
> Currently, the CEP library does not support Java 8 lambdas to be used as
> {{select}} or {{flatSelect}} function. The problem is that the
> {{TypeExtractor}} has different semantics when calling
> {{TypeExtractor.getUnaryOperatorReturnType}} either with a Java 8 lambda or
> an instance of an UDF function.
> To illustrate the problem assume we have the following UDF function
> {code}
> public interface MyFunction[T, O] {
> O foobar(Map<String, T> inputElements);
> }
> {code}
> When calling the {{TypeExtractor}} with an anonymous class which implements
> this interface, the first type parameter is considered being the input type
> of the function, namely {{T}}.
> In contrast, when providing a Java 8 lambda for this interface, the
> {{TypeExtractor}} will see an input type of {{Map<String, T>}}.
> This problem also occurs with a {{FlatMapFunction}} whose first type argument
> is {{T}} but whose first parameter of a Java 8 lambda is {{Iterable<T>}}. In
> order to solve the problem here, the
> {{TypeExtractor.getUnaryOperatorReturnType}} method has the parameters
> {{hasIterable}} and {{hasCollector}}. If these values are {{true}}, then a
> special code path is taken (in case of a Java 8 lambda), where the input type
> is compared to the first type argument of the first input parameter of the
> lambda (here an {{Iterable<T>}}). This hand-knitted solution does not
> generalize well, as it will fail for all parameterized types which have the
> input type at a different position (e.g. {{Map<String, T>}}.
> In order to solve the problem, I propose to generalize the
> {{getUnaryOperatorReturnType}} a little bit so that one can specify at which
> position the input type is specified by a parameterized type.
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