Seems fair. This should not immediately fail, but also only give a
"MissingTypeInfo" so that type hints would work.
The error message is also wrong, btw: It should state that raw types are
not supported.
On Fri, Aug 21, 2015 at 1:02 PM, Matthias J. Sax <
mj...@informatik.hu-berlin.de> wrote:
> Hi,
>
> I changed the WordCount example as below and I am wondering, why this
> does not work. Looking at the Flink internal implemenation, it make
> sense that it fails. However, from an API point of view it should work.
> Is this a bug or do I miss understand the semantic of .returns(...)?
>
> The change is about type inference and generics. I removed the generic
> type information in tokenizer and provide the output type via
> returns(...) methods. Whoever, I get an exception (see below).
>
> Tokenizer is change to this (removed generics and added cast to String):
>
> > public static final class Tokenizer implements FlatMapFunction {
> > public void flatMap(Object value, Collector out) {
> > String[] tokens = ((String)
> value).toLowerCase().split("\\W+");
> > for (String token : tokens) {
> > if (token.length() > 0) {
> > out.collect(new Tuple2<String,
> Integer>(token, 1));
> > }
> > }
> > }
> > }
>
> I added call to "returns(....)" here:
>
> > DataSet<Tuple2<String, Integer>> counts =
> > text.flatMap(new Tokenizer()).returns("Tuple2<String,Integer>")
> > .groupBy(0).sum(1);
>
> The exception is:
>
> > Exception in thread "main" java.lang.IllegalArgumentException: The types
> of the interface org.apache.flink.api.common.functions.FlatMapFunction
> could not be inferred. Support for synthetic interfaces, lambdas, and
> generic types is limited at this point.
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.getParameterType(TypeExtractor.java:686)
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.getParameterTypeFromGenericType(TypeExtractor.java:710)
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.getParameterType(TypeExtractor.java:673)
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.privateCreateTypeInfo(TypeExtractor.java:365)
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:279)
> > at
> org.apache.flink.api.java.typeutils.TypeExtractor.getFlatMapReturnTypes(TypeExtractor.java:120)
> > at org.apache.flink.api.java.DataSet.flatMap(DataSet.java:262)
> > at
> org.apache.flink.examples.java.wordcount.WordCount.main(WordCount.java:69)
>
>
> -Matthias
>
>
