reduce duplication of FunctionN as scala.runtime.java8.JFunction

[adriaanm]

We'll still need something for void-return functions. First stab: scala/scala@0db3f41

[retronym]

The JProcedureN classes aren't actually used by the current backend, we create an "$adapted" method that converts void to BoxedUnit.

The difficulty is with specialization.

import scala.*;
import java.util.Arrays;

public class Test {
    private static void printApplyMethods() {
         Arrays.stream(Thread.currentThread().getStackTrace()).filter(x -> x.getMethodName().startsWith("apply")).forEach(System.out::println);
         System.out.println();
    }
    public static void main(String[] args) {
        Function0<String> f0_String = () -> "";
        f0_String.apply();
        Function0<? extends Object> f0_Object = f0_String;
        f0_Object.apply();

        Function0$mcI$sp f0_int = () -> {printApplyMethods(); return 42;};
        f0_int.apply();
        f0_int.apply$mcI$sp(); // Routes through boxing in `scala.Function0.apply$mcI$sp`
        Function0<Integer> f0_Integer = (Function0<Integer>) (Object) f0_int;
        f0_Integer.apply();

        Function1<String, String> f1_String_String = x -> x;
        f1_String_String.apply("");
        Function1$mcII$sp f1_int_int = x -> {printApplyMethods(); return 42;};
        f1_int_int.apply$mcII$sp(0); // Routes through boxing in `scala.Function1.apply$mcII$sp`
        Function1<Integer, Integer> f1_Integer_Integer = (Function1<Integer, Integer>) (Object) f1_int_int;
        f1_Integer_Integer.apply(42);
    }
}

javac -d . -classpath build/quick/classes/library sandbox/Test.java && qscala -J-XX:+UnlockDiagnosticVMOptions -J-XX:+ShowHiddenFrames Test
Note: sandbox/Test.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
Test$$Lambda$125/1982791261.apply(<Unknown>:1000000)
scala.reflect.internal.util.ScalaClassLoader$$Lambda$123/1993134103.apply(<Unknown>:1000008)

Test$$Lambda$125/1982791261.apply(<Unknown>:1000000)
scala.Function0.apply$mcI$sp(Function0.scala:34)
scala.reflect.internal.util.ScalaClassLoader$$Lambda$123/1993134103.apply(<Unknown>:1000008)

Test$$Lambda$125/1982791261.apply(<Unknown>:1000000)
scala.reflect.internal.util.ScalaClassLoader$$Lambda$123/1993134103.apply(<Unknown>:1000008)

Test$$Lambda$129/1763847188.apply(<Unknown>:1000001)
scala.Function1.apply$mcII$sp(Function1.scala:36)
scala.reflect.internal.util.ScalaClassLoader$$Lambda$123/1993134103.apply(<Unknown>:1000008)

Test$$Lambda$129/1763847188.apply(<Unknown>:1000001)
scala.reflect.internal.util.ScalaClassLoader$$Lambda$123/1993134103.apply(<Unknown>:1000008)

An easy first step would be to change non-specialized lambdas to directly use FunctionN.

[retronym]

Related: #36

[adriaanm]

Right you are. I misinterpreted the crash.

[retronym]

This is largely fixed in scala/scala#4971. I'm going to close this and open a followup (low priority) ticket for specialized FunctionN.