[GROOVY-10979] Cannot provide method reference to a type parameter instantiated with a SAM type

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Static Type Checker
• Assignee: Unassigned
• Reporter: Thodoris Sotiropoulos
• Created: 21/Mar/23 10:12
• Updated: 19/Sep/23 19:56

Description

I have the following program

import java.util.function.*;
import java.util.stream.*;

public class Test {

    public static void test() {
      Stream<Number> x = null;
      BiFunction<Function<String, Integer>, Number, Function<String, Integer>> y = null;
      BinaryOperator<Function<String, Integer>> z = null;

      x.<Function<String, Integer>>reduce(Test::m, y, z);  // fails
      x.reduce(Test::m, y, z);   // fails
      x.reduce((d) -> 1, y, z);   // works

    }

    public static Integer m(String x) { return 1; }
}

Actual behavior

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 12: The argument is a method reference, but the parameter type is not a functional interface
 @ line 12, column 43.
   ction<String, Integer>>reduce(Test::m, y
                                 ^

test.groovy: 13: The argument is a method reference, but the parameter type is not a functional interface
 @ line 13, column 16.
         x.reduce(Test::m, y, z);   // fails
                  ^

2 errors

Expected behavior

Compile successfully

Tested against master (commit: 55c6edfd81a64ce759357a3976070c0811bff637)

Issue Links

• relates to: GROOVY-11181 Improve STC error message for non-functional interface