Using RC2, zip variant is 10x slower (1500 ms vs. 150 ms)

ZipSpeedTest.java

import javaslang.collection.List;
import org.junit.Test;

import java.util.Iterator;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class ZipSpeedTest {

    private static final java.util.List<String> JAVA_LIST = IntStream.range(0, 1_000_000).mapToObj(String::valueOf).collect(Collectors.toList());
    private static final java.lang.Iterable<String> JAVA_ITERABLE = JAVA_LIST::iterator;
    private static final List<String> SLANG_LIST = List.range(0, 1_000_000).map(String::valueOf);

    @Test
    public void zip() {
        long startTime = System.currentTimeMillis();

        SLANG_LIST.zip(JAVA_ITERABLE).map(t -> t._1 + t._2);

        System.out.println("Variant 'zip': " + (System.currentTimeMillis() - startTime));
    }

    @Test
    public void next() {
        long startTime = System.currentTimeMillis();

        Iterator<String> it = JAVA_ITERABLE.iterator();
        SLANG_LIST.map(e -> e + it.next());

        System.out.println("Variant 'next': " + (System.currentTimeMillis() - startTime));
    }

}