add asLeftOptional, more type flexibility for toValidList

Author: h908714124

src/main/java/io/jbock/util/Either.java

@@ -59,7 +59,7 @@ public static <L, R> Either<L, R> right(R value) {
      * @return a Right containing all RHS values in the stream,
      *         or, if an LHS value exists, a Left containing the first such value
      */
-    public static <L, R> Collector<Either<L, R>, ?, Either<L, List<R>>> toValidList() {
+    public static <L, R> Collector<Either<? extends L, ? extends R>, ?, Either<L, List<R>>> toValidList() {
         return new ValidatingCollector<>();
     }
 
@@ -74,10 +74,28 @@ public static <L, R> Either<L, R> right(R value) {
      * @return a list of the RHS values in the stream,
      *         or, if an LHS value exists, a nonempty list of all LHS values
      */
-    public static <L, R> Collector<Either<L, R>, ?, Either<List<L>, List<R>>> toValidListAll() {
+    public static <L, R> Collector<Either<? extends L, ? extends R>, ?, Either<List<L>, List<R>>> toValidListAll() {
         return new ValidatingCollectorAll<>();
     }
 
+    /**
+     * If the provided list is empty, returns an empty {@link Optional}.
+     * Otherwise, returns an {@code Optional} containing the list.
+     *
+     * @param failures a failures
+     * @param <L> the type of the members of the failures
+     * @return an {@code Optional} which is empty if and only if {@code failures}
+     *         is empty
+     */
+    public static <L> Optional<List<L>> asLeftOptional(List<? extends L> failures) {
+        if (failures.isEmpty()) {
+            return Optional.empty();
+        }
+        @SuppressWarnings("unchecked")
+        List<L> result = (List<L>) failures;
+        return Optional.of(result);
+    }
+
     /**
      * If this is a Right, returns a Right containing the result of applying
      * the mapper function to the RHS value.

src/main/java/io/jbock/util/ValidatingCollector.java

@@ -15,14 +15,14 @@
  * @param <L> the type of the LHS values in the stream
  * @param <R> the type of the RHS values in the stream
  */
-final class ValidatingCollector<L, R> implements Collector<Either<L, R>, ValidatingCollector.Acc<L, R>, Either<L, List<R>>> {
+final class ValidatingCollector<L, R> implements Collector<Either<? extends L, ? extends R>, ValidatingCollector.Acc<L, R>, Either<L, List<R>>> {
 
     static final class Acc<L, R> {
 
         private L left;
         private final List<R> right = new ArrayList<>();
 
-        void accumulate(Either<L, R> either) {
+        void accumulate(Either<? extends L, ? extends R> either) {
             if (left != null) {
                 return;
             }
@@ -56,7 +56,7 @@ public Supplier<Acc<L, R>> supplier() {
     }
 
     @Override
-    public BiConsumer<Acc<L, R>, Either<L, R>> accumulator() {
+    public BiConsumer<Acc<L, R>, Either<? extends L, ? extends R>> accumulator() {
         return Acc::accumulate;
     }
 

src/main/java/io/jbock/util/ValidatingCollectorAll.java

@@ -15,14 +15,14 @@
  * @param <L> the type of the LHS values in the stream
  * @param <R> the type of the RHS values in the stream
  */
-final class ValidatingCollectorAll<L, R> implements Collector<Either<L, R>, ValidatingCollectorAll.Acc<L, R>, Either<List<L>, List<R>>> {
+final class ValidatingCollectorAll<L, R> implements Collector<Either<? extends L, ? extends R>, ValidatingCollectorAll.Acc<L, R>, Either<List<L>, List<R>>> {
 
     static final class Acc<L, R> {
 
         private final List<L> left = new ArrayList<>();
         private final List<R> right = new ArrayList<>();
 
-        void accumulate(Either<L, R> either) {
+        void accumulate(Either<? extends L, ? extends R> either) {
             if (!left.isEmpty()) {
                 either.ifLeftOrElse(left::add, r -> {
                 });
@@ -58,7 +58,7 @@ public Supplier<Acc<L, R>> supplier() {
     }
 
     @Override
-    public BiConsumer<Acc<L, R>, Either<L, R>> accumulator() {
+    public BiConsumer<Acc<L, R>, Either<? extends L, ? extends R>> accumulator() {
         return Acc::accumulate;
     }