Required argument type in AbstractVertexFrame.traverse() does not allow for anonymous traversals

alvanson commented 7 years ago

In the Node.java reproduced below, using Ferma 3.0.2 and tinkergraph-gremlin 3.2.3 on OpenJDK 8u121-b13, attempting to use Node.traverse() with an anonymous traversal (__.out("parent")) results in the following compile-time error (change the call to traverse1() back to traverse() first):

Node.java:[56,46] error: incompatible types: no instance(s) of type variable(s) A exist so that GraphTraversal<A,Vertex> conforms to Traversal<?,CAP#1>

Changing the argument type of traverse() from Function<GraphTraversal<? extends Vertex, ? extends Vertex>, GraphTraversal<?, ?>> to Function<GraphTraversal<Vertex, Vertex>, GraphTraversal<?, ?>> seems to correct the issue. Following the types through the current TinkerPop API, input.V(getElement().id()) returns type GraphTraversal<Vertex, Vertex> so I believe it is sufficient to require traverser to have type Function<GraphTraversal<Vertex, Vertex>, GraphTraversal<?, ?>>.

I imagine a similar issue exists with AbstractEdgeFrame.

Node.java:

package com.syncleus.ferma.issues;

import com.syncleus.ferma.AbstractVertexFrame;
import com.syncleus.ferma.DelegatingFramedGraph;
import com.syncleus.ferma.FramedGraph;
import com.syncleus.ferma.Traversable;
import com.syncleus.ferma.annotations.Adjacency;
import com.syncleus.ferma.annotations.Property;
import javax.annotation.Nullable;
import java.util.function.Function;
import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal;
import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversalSource;
import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.__;
import org.apache.tinkerpop.gremlin.structure.Direction;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.Vertex;
import org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerGraph;

public abstract class Node extends AbstractVertexFrame {

    public static void main(String[] args) {
        // create new graph
        Graph graph = TinkerGraph.open();
        FramedGraph fg = new DelegatingFramedGraph(graph, true, true);
        // add five nodes (vertices)
        Node[] nodes = new Node[5];
        for (int i = 0; i < nodes.length; i++) {
            nodes[i] = fg.addFramedVertex(Node.class);
            nodes[i].setName("Node" + i);
        }
        // Node0 <- Node1 <- ... <- Node4
        for (int i = 1; i < nodes.length; i++) {
            nodes[i].setParent(nodes[i - 1]);
        }
        // ask Node3 for its grandparent (Node1)
        System.out.println(nodes[3].getGrandParent());
    }

    @Property("name")
    public abstract String getName();

    @Property("name")
    public abstract void setName(String name);

    @Adjacency(label = "parent", direction = Direction.OUT)
    public abstract Node getParent();

    public void setParent(Node parent) {
        // node can only have one parent
        setLinkOut(parent, "parent");
    }

    public Node getGrandParent() {
        // with traverse(): Node.java:[55,46] error: incompatible types: no instance(s) of type variable(s) A exist so that GraphTraversal<A,Vertex> conforms to Traversal<?,CAP#1>
        return traverse1((v) -> v.repeat(__.out("parent")).times(2)).next(Node.class);
    }

    public <T extends Traversable<?, ?>> T traverse1(final Function<GraphTraversal<Vertex, Vertex>, GraphTraversal<?, ?>> traverser) {
        return this.getGraph().traverse(new Function<GraphTraversalSource, GraphTraversal<?, ?>>() {
            @Nullable
            @Override
            public GraphTraversal<?, ?> apply(@Nullable final GraphTraversalSource input) {
                return traverser.apply(input.V(getElement().id()));
            }
        });
    }

}