performance improvements for filter and mapLeft

Author: h908714124

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

@@ -116,9 +116,7 @@ public final <R2> Either<L, R2> flatMap(
      * @param predicate a function that acts as a filter predicate
      * @return filter result
      */
-    public final Either<L, R> filter(Function<? super R, LeftOptional<? extends L>> predicate) {
-        return fold(Either::left, r -> narrow(predicate.apply(r).orElseRight(() -> r)));
-    }
+    public abstract Either<L, R> filter(Function<? super R, LeftOptional<? extends L>> predicate);
 
     /**
      * If this is a Left, returns a Left containing the result of applying the mapper function to the LHS value.
@@ -129,9 +127,7 @@ public final Either<L, R> filter(Function<? super R, LeftOptional<? extends L>>
      * @return an equivalent instance if this is a Right, otherwise a Left containing
      *         the result of applying {@code mapper} to the LHS value
      */
-    public final <L2> Either<L2, R> mapLeft(Function<? super L, ? extends L2> mapper) {
-        return fold(l -> left(mapper.apply(l)), Either::right);
-    }
+    public abstract <L2> Either<L2, R> mapLeft(Function<? super L, ? extends L2> mapper);
 
     /**
      * If this is a Left, returns the result of applying the mapper function to the LHS value.

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

@@ -32,6 +32,16 @@ public Optional<R> getRight() {
         return Optional.empty();
     }
 
+    @Override
+    public Either<L, R> filter(Function<? super R, LeftOptional<? extends L>> predicate) {
+        return same();
+    }
+
+    @Override
+    public <L2> Either<L2, R> mapLeft(Function<? super L, ? extends L2> mapper) {
+        return create(mapper.apply(value));
+    }
+
     @Override
     public <L2> Either<L2, R> flatMapLeft(Function<? super L, ? extends Either<? extends L2, ? extends R>> mapper) {
         return narrow(mapper.apply(value));

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

@@ -32,6 +32,20 @@ public Optional<R> getRight() {
         return Optional.of(value);
     }
 
+    @Override
+    public Either<L, R> filter(Function<? super R, LeftOptional<? extends L>> predicate) {
+        LeftOptional<? extends L> test = predicate.apply(value);
+        if (test.isEmpty()) {
+            return same();
+        }
+        return Left.create(test.orElseThrow());
+    }
+
+    @Override
+    public <L2> Either<L2, R> mapLeft(Function<? super L, ? extends L2> mapper) {
+        return same();
+    }
+
     @Override
     public <L2> Either<L2, R> flatMapLeft(Function<? super L, ? extends Either<? extends L2, ? extends R>> mapper) {
         return same();