Groovy closures and overloaded methods with functional parameters

Question

I get Ambiguous error when I try to use a code which contains overloaded methods with functional arguments.

I wrote a small snippet which shows an ambiguous behavior:

import java.util.function.BiConsumer
import java.util.function.Consumer

class Test {

    static void main(String... args) {
        execute({ x -> println("Consumer") })
        execute({ x, y -> println("BiConsumer") })
    }

    static void execute(Consumer<Integer> c) {
        c.accept(100)
    }

    static void execute(BiConsumer<Integer, Integer> c) {
        c.accept(1, 2)
    }
}

Output (2.4.9 groovy):

    Exception in thread "main" groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method Test#execute.
Cannot resolve which method to invoke for [class Test$_main_closure1] due to overlapping prototypes between:
    [interface java.util.function.BiConsumer]
    [interface java.util.function.Consumer]
    at groovy.lang.MetaClassImpl.chooseMostSpecificParams(MetaClassImpl.java:3268)
    at groovy.lang.MetaClassImpl.chooseMethodInternal(MetaClassImpl.java:3221)
    at groovy.lang.MetaClassImpl.chooseMethod(MetaClassImpl.java:3164)
    at groovy.lang.MetaClassImpl.pickStaticMethod(MetaClassImpl.java:1516)
    at groovy.lang.MetaClassImpl.retrieveStaticMethod(MetaClassImpl.java:1412)
    at org.codehaus.groovy.vmplugin.v7.Selector$MethodSelector.chooseMeta(Selector.java:553)
    at org.codehaus.groovy.vmplugin.v7.Selector$MethodSelector.setCallSiteTarget(Selector.java:954)
    at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:228)
    at Test.main(Test.groovy:7)

But it works with java-lambdas and I don't understand how to use a groovy-closures in this situation.

Answer 1

You need to put as XXX after your closures to give the runtime a clue where you want to go

    execute({ x -> println("Consumer") } as Consumer)
    execute({ x, y -> println("BiConsumer") } as BiConsumer)

Should do it

Answer 2

Maybe using a Closure:

execute(Closure <Integer> c) {
  c (10)
}

execute (Closure <Integer, Integer> c) {
  c (10, 30)
}