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https://issues.apache.org/jira/browse/FLINK-1062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14118201#comment-14118201
]
Stephan Ewen commented on FLINK-1062:
-------------------------------------
Here is some of my old playground code that gets all generic types from lambdas
in a pretty safe way:
{code}
public class ClassWithLambdas {
public static void main(String[] args) throws Exception {
SomeFunction func = (map) ->
Arrays.asList(map.get("hello").iterator().next().longValue());
SomeFunction2<Double, Long> func2 = (map) ->
Arrays.asList(map.get("hello").iterator().next().longValue());
SerializedLambda sl1 = getSerializedLambda(func);
SerializedLambda sl2 = getSerializedLambda(func2);
Method m1 = getLambdaMethod(sl1);
Method m2 = getLambdaMethod(sl2);
System.out.println(m1);
System.out.println(m1.getGenericReturnType());
for (Type t : m1.getGenericParameterTypes()) {
System.out.println(t);
}
System.out.println("\n-----\n");
System.out.println(m2);
System.out.println(m2.getGenericReturnType());
for (Type t : m2.getGenericParameterTypes()) {
System.out.println(t);
}
}
//
--------------------------------------------------------------------------------------------
public static SerializedLambda getSerializedLambda(Object function) {
if (function == null || !(function instanceof
java.io.Serializable)) {
throw new IllegalArgumentException();
}
for (Class<?> clazz = function.getClass(); clazz != null; clazz
= clazz.getSuperclass()) {
try {
Method replaceMethod =
clazz.getDeclaredMethod("writeReplace");
replaceMethod.setAccessible(true);
Object serializedForm = replaceMethod.invoke(function);
if (serializedForm instanceof SerializedLambda) {
return (SerializedLambda) serializedForm;
}
}
catch (NoSuchMethodError e) {
// fall through the loop and try the next class
}
catch (Throwable t) {
throw new RuntimeException("Error while extracting
serialized lambda", t);
}
}
return null;
}
public static Method getLambdaMethod(SerializedLambda lambda) throws
Exception {
String implClassName = lambda.getImplClass().replace('/', '.');
Class<?> implClass = Class.forName(implClassName);
String lambdaName = lambda.getImplMethodName();
for (Method m : implClass.getDeclaredMethods()) {
if (m.getName().equals(lambdaName)) {
return m;
}
}
return null;
}
//
--------------------------------------------------------------------------------------------
public static interface SomeFunction extends java.io.Serializable {
List<Long> applyTheFunction(Map<String, Set<Double>> theMap)
throws IOException;
}
public static interface SomeFunction2<I, O> extends
java.io.Serializable {
List<O> applyTheFunction(Map<String, Set<I>> theMap) throws
IOException;
}
}
{code}
> Type Extraction for Lambdas
> ---------------------------
>
> Key: FLINK-1062
> URL: https://issues.apache.org/jira/browse/FLINK-1062
> Project: Flink
> Issue Type: Improvement
> Components: Java API
> Affects Versions: 0.7-incubating
> Reporter: Stephan Ewen
> Assignee: Timo Walther
> Fix For: 0.7-incubating
>
>
> Lambdas currently work only for {{filter}} and {{reduce(a,b)}}, because
> Lambda type extraction is not in place right now.
> We need to extend the type extraction for lambdas to support the other
> functions.
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