[ https://issues.apache.org/jira/browse/FLINK-3681?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Till Rohrmann closed FLINK-3681. -------------------------------- 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. -- This message was sent by Atlassian JIRA (v6.3.4#6332)