From a367d0f2e4cdbb070dea2e07d38ab5ae4c2b4ab3 Mon Sep 17 00:00:00 2001
From: Jose Luis Leon <joseluis5000l@gmail.com>
Date: Mon, 6 Nov 2023 01:50:18 -0500
Subject: [PATCH] chore(either): Simplify Either implementation (#217)

---
 .../io/github/joselion/maybe/util/Either.java | 166 ++++++------------
 .../io/github/joselion/maybe/util/Either.java | 166 ++++++------------
 2 files changed, 112 insertions(+), 220 deletions(-)

diff --git a/src/main/java/io/github/joselion/maybe/util/Either.java b/src/main/java/io/github/joselion/maybe/util/Either.java
index ee1dfab..65b9c08 100644
--- a/src/main/java/io/github/joselion/maybe/util/Either.java
+++ b/src/main/java/io/github/joselion/maybe/util/Either.java
@@ -49,19 +49,37 @@ static <L, R> Either<L, R> ofRight(final R value) {
     return new Right<>(value);
   }
 
+  /**
+   * Terminal operator. Unwraps the {@code Either} to obtain the wrapped value.
+   * Since there's no possible way for the compiler to know which one is
+   * present ({@code Left} or {@code Right}), you need to provide a handler for
+   * both cases. Only the handler with the value present is used to unwrap and
+   * return the value.
+   *
+   * @param <T> the type of the returned value
+   * @param onLeft a function to handle the left value if present
+   * @param onRight a function to handle the right value if present
+   * @return either the left or the right handled value
+   */
+  <T> T unwrap(Function<L, T> onLeft, Function<R, T> onRight);
+
   /**
    * Returns true if the {@code Left} value is present, false otherwise.
    *
    * @return true if left is present, false otherwise
    */
-  boolean isLeft();
+  default boolean isLeft() {
+    return unwrap(left -> true, right -> false);
+  }
 
   /**
    * Returns true if the {@code Right} value is present, false otherwise.
    *
    * @return true if right is present, false otherwise
    */
-  boolean isRight();
+  default boolean isRight() {
+    return unwrap(left -> false, rigth -> true);
+  }
 
   /**
    * Run an effect if the {@code Left} value is present. Does nothing otherwise.
@@ -69,7 +87,15 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param effect a consumer function that receives the left value
    * @return the same {@code Either} instance
    */
-  Either<L, R> doOnLeft(Consumer<L> effect);
+  default Either<L, R> doOnLeft(final Consumer<L> effect) {
+    return unwrap(
+      left -> {
+        effect.accept(left);
+        return Either.ofLeft(left);
+      },
+      Either::ofRight
+    );
+  }
 
   /**
    * Run an effect if the {@code Right} value is present. Does nothing otherwise.
@@ -77,7 +103,15 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param effect effect a consumer function that receives the right value
    * @return the same {@code Either} instance
    */
-  Either<L, R> doOnRight(Consumer<R> effect);
+  default Either<L, R> doOnRight(final Consumer<R> effect) {
+    return unwrap(
+      Either::ofLeft,
+      right -> {
+        effect.accept(right);
+        return Either.ofRight(right);
+      }
+    );
+  }
 
   /**
    * Map the {@code Left} value to another if present. Does nothing otherwise.
@@ -86,7 +120,12 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param mapper a function that receives the left value and returns another
    * @return an {@code Either} instance with the mapped left value
    */
-  <T> Either<T, R> mapLeft(Function<L, T> mapper);
+  default <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
+    return unwrap(
+      left -> Either.ofLeft(mapper.apply(left)),
+      Either::ofRight
+    );
+  }
 
   /**
    * Map the {@code Right} value to another if present. Does nothing otherwise.
@@ -95,7 +134,12 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param mapper a function that receives the right value and returns another
    * @return an {@code Either} instance with the mapped right value
    */
-  <T> Either<L, T> mapRight(Function<R, T> mapper);
+  default <T> Either<L, T> mapRight(final Function<R, T> mapper) {
+    return unwrap(
+      Either::ofLeft,
+      right -> Either.ofRight(mapper.apply(right))
+    );
+  }
 
   /**
    * Terminal operator. Returns the {@code Left} value if present. Otherwise,
@@ -104,7 +148,9 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param fallback the value to return if left is not present
    * @return the left value or a fallback
    */
-  L leftOrElse(L fallback);
+  default L leftOrElse(final L fallback) {
+    return unwrap(Function.identity(), rigth -> fallback);
+  }
 
   /**
    * Terminal operator. Returns the {@code Right} value if present. Otherwise,
@@ -113,21 +159,9 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param fallback the value to return if right is not present
    * @return the right value or a fallback
    */
-  R rightOrElse(R fallback);
-
-  /**
-   * Terminal operator. Unwraps the {@code Either} to obtain the wrapped value.
-   * Since there's no possible way for the compiler to know which one is
-   * present ({@code Left} or {@code Right}), you need to provide a handler for
-   * both cases. Only the handler with the value present is used to unwrap and
-   * return the value.
-   *
-   * @param <T> the type of the returned value
-   * @param onLeft a function to handle the left value if present
-   * @param onRight a function to handle the right value if present
-   * @return either the left or the right handled value
-   */
-  <T> T unwrap(Function<L, T> onLeft, Function<R, T> onRight);
+  default R rightOrElse(final R fallback) {
+    return unwrap(left -> fallback, Function.identity());
+  }
 
   /**
    * Terminal operator. Returns the {@code Left} value if present. Otherwise,
@@ -193,50 +227,6 @@ L value() {
       return this.value;
     }
 
-    @Override
-    public boolean isLeft() {
-      return true;
-    }
-
-    @Override
-    public boolean isRight() {
-      return false;
-    }
-
-    @Override
-    public Either<L, R> doOnLeft(final Consumer<L> effect) {
-      effect.accept(this.value);
-
-      return this;
-    }
-
-    @Override
-    public Either<L, R> doOnRight(final Consumer<R> effect) {
-      return this;
-    }
-
-    @Override
-    public <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
-      final var mappedLeft = mapper.apply(this.value);
-
-      return new Left<>(mappedLeft);
-    }
-
-    @Override
-    public <T> Either<L, T> mapRight(final Function<R, T> mapper) {
-      return new Left<>(this.value);
-    }
-
-    @Override
-    public L leftOrElse(final L fallback) {
-      return this.value;
-    }
-
-    @Override
-    public R rightOrElse(final R fallback) {
-      return fallback;
-    }
-
     @Override
     public <T> T unwrap(final Function<L, T> onLeft, final Function<R, T> onRight) {
       return onLeft.apply(this.value);
@@ -291,50 +281,6 @@ R value() {
       return this.value;
     }
 
-    @Override
-    public boolean isLeft() {
-      return false;
-    }
-
-    @Override
-    public boolean isRight() {
-      return true;
-    }
-
-    @Override
-    public Either<L, R> doOnLeft(final Consumer<L> effect) {
-      return this;
-    }
-
-    @Override
-    public Either<L, R> doOnRight(final Consumer<R> effect) {
-      effect.accept(this.value);
-
-      return this;
-    }
-
-    @Override
-    public <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
-      return new Right<>(this.value);
-    }
-
-    @Override
-    public <T> Either<L, T> mapRight(final Function<R, T> mapper) {
-      final var mappedRight = mapper.apply(this.value);
-
-      return new Right<>(mappedRight);
-    }
-
-    @Override
-    public L leftOrElse(final L fallback) {
-      return fallback;
-    }
-
-    @Override
-    public R rightOrElse(final R fallback) {
-      return this.value;
-    }
-
     @Override
     public <T> T unwrap(final Function<L, T> onLeft, final Function<R, T> onRight) {
       return onRight.apply(this.value);
diff --git a/src/main/java17/io/github/joselion/maybe/util/Either.java b/src/main/java17/io/github/joselion/maybe/util/Either.java
index d5ff374..226f170 100644
--- a/src/main/java17/io/github/joselion/maybe/util/Either.java
+++ b/src/main/java17/io/github/joselion/maybe/util/Either.java
@@ -49,19 +49,37 @@ static <L, R> Either<L, R> ofRight(final R value) {
     return new Right<>(value);
   }
 
+  /**
+   * Terminal operator. Unwraps the {@code Either} to obtain the wrapped value.
+   * Since there's no possible way for the compiler to know which one is
+   * present ({@code Left} or {@code Right}), you need to provide a handler for
+   * both cases. Only the handler with the value present is used to unwrap and
+   * return the value.
+   *
+   * @param <T> the type of the returned value
+   * @param onLeft a function to handle the left value if present
+   * @param onRight a function to handle the right value if present
+   * @return either the left or the right handled value
+   */
+  <T> T unwrap(Function<L, T> onLeft, Function<R, T> onRight);
+
   /**
    * Returns true if the {@code Left} value is present, false otherwise.
    *
    * @return true if left is present, false otherwise
    */
-  boolean isLeft();
+  default boolean isLeft() {
+    return unwrap(left -> true, right -> false);
+  }
 
   /**
    * Returns true if the {@code Right} value is present, false otherwise.
    *
    * @return true if right is present, false otherwise
    */
-  boolean isRight();
+  default boolean isRight() {
+    return unwrap(left -> false, rigth -> true);
+  }
 
   /**
    * Run an effect if the {@code Left} value is present. Does nothing otherwise.
@@ -69,7 +87,15 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param effect a consumer function that receives the left value
    * @return the same {@code Either} instance
    */
-  Either<L, R> doOnLeft(Consumer<L> effect);
+  default Either<L, R> doOnLeft(final Consumer<L> effect) {
+    return unwrap(
+      left -> {
+        effect.accept(left);
+        return Either.ofLeft(left);
+      },
+      Either::ofRight
+    );
+  }
 
   /**
    * Run an effect if the {@code Right} value is present. Does nothing otherwise.
@@ -77,7 +103,15 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param effect effect a consumer function that receives the right value
    * @return the same {@code Either} instance
    */
-  Either<L, R> doOnRight(Consumer<R> effect);
+  default Either<L, R> doOnRight(final Consumer<R> effect) {
+    return unwrap(
+      Either::ofLeft,
+      right -> {
+        effect.accept(right);
+        return Either.ofRight(right);
+      }
+    );
+  }
 
   /**
    * Map the {@code Left} value to another if present. Does nothing otherwise.
@@ -86,7 +120,12 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param mapper a function that receives the left value and returns another
    * @return an {@code Either} instance with the mapped left value
    */
-  <T> Either<T, R> mapLeft(Function<L, T> mapper);
+  default <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
+    return unwrap(
+      left -> Either.ofLeft(mapper.apply(left)),
+      Either::ofRight
+    );
+  }
 
   /**
    * Map the {@code Right} value to another if present. Does nothing otherwise.
@@ -95,7 +134,12 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param mapper a function that receives the right value and returns another
    * @return an {@code Either} instance with the mapped right value
    */
-  <T> Either<L, T> mapRight(Function<R, T> mapper);
+  default <T> Either<L, T> mapRight(final Function<R, T> mapper) {
+    return unwrap(
+      Either::ofLeft,
+      right -> Either.ofRight(mapper.apply(right))
+    );
+  }
 
   /**
    * Terminal operator. Returns the {@code Left} value if present. Otherwise,
@@ -104,7 +148,9 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param fallback the value to return if left is not present
    * @return the left value or a fallback
    */
-  L leftOrElse(L fallback);
+  default L leftOrElse(final L fallback) {
+    return unwrap(Function.identity(), rigth -> fallback);
+  }
 
   /**
    * Terminal operator. Returns the {@code Right} value if present. Otherwise,
@@ -113,21 +159,9 @@ static <L, R> Either<L, R> ofRight(final R value) {
    * @param fallback the value to return if right is not present
    * @return the right value or a fallback
    */
-  R rightOrElse(R fallback);
-
-  /**
-   * Terminal operator. Unwraps the {@code Either} to obtain the wrapped value.
-   * Since there's no possible way for the compiler to know which one is
-   * present ({@code Left} or {@code Right}), you need to provide a handler for
-   * both cases. Only the handler with the value present is used to unwrap and
-   * return the value.
-   *
-   * @param <T> the type of the returned value
-   * @param onLeft a function to handle the left value if present
-   * @param onRight a function to handle the right value if present
-   * @return either the left or the right handled value
-   */
-  <T> T unwrap(Function<L, T> onLeft, Function<R, T> onRight);
+  default R rightOrElse(final R fallback) {
+    return unwrap(left -> fallback, Function.identity());
+  }
 
   /**
    * Terminal operator. Returns the {@code Left} value if present. Otherwise,
@@ -187,50 +221,6 @@ record Left<L, R>(L value) implements Either<L, R> {
       Objects.requireNonNull(value, "An Either cannot be created with a null value");
     }
 
-    @Override
-    public boolean isLeft() {
-      return true;
-    }
-
-    @Override
-    public boolean isRight() {
-      return false;
-    }
-
-    @Override
-    public Either<L, R> doOnLeft(final Consumer<L> effect) {
-      effect.accept(this.value);
-
-      return this;
-    }
-
-    @Override
-    public Either<L, R> doOnRight(final Consumer<R> effect) {
-      return this;
-    }
-
-    @Override
-    public <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
-      final var mappedLeft = mapper.apply(this.value);
-
-      return new Left<>(mappedLeft);
-    }
-
-    @Override
-    public <T> Either<L, T> mapRight(final Function<R, T> mapper) {
-      return new Left<>(this.value);
-    }
-
-    @Override
-    public L leftOrElse(final L fallback) {
-      return this.value;
-    }
-
-    @Override
-    public R rightOrElse(final R fallback) {
-      return fallback;
-    }
-
     @Override
     public <T> T unwrap(final Function<L, T> onLeft, final Function<R, T> onRight) {
       return onLeft.apply(this.value);
@@ -278,50 +268,6 @@ record Right<L, R>(R value) implements Either<L, R> {
       Objects.requireNonNull(value, "An Either cannot be created with a null value");
     }
 
-    @Override
-    public boolean isLeft() {
-      return false;
-    }
-
-    @Override
-    public boolean isRight() {
-      return true;
-    }
-
-    @Override
-    public Either<L, R> doOnLeft(final Consumer<L> effect) {
-      return this;
-    }
-
-    @Override
-    public Either<L, R> doOnRight(final Consumer<R> effect) {
-      effect.accept(this.value);
-
-      return this;
-    }
-
-    @Override
-    public <T> Either<T, R> mapLeft(final Function<L, T> mapper) {
-      return new Right<>(this.value);
-    }
-
-    @Override
-    public <T> Either<L, T> mapRight(final Function<R, T> mapper) {
-      final var mappedRight = mapper.apply(this.value);
-
-      return new Right<>(mappedRight);
-    }
-
-    @Override
-    public L leftOrElse(final L fallback) {
-      return fallback;
-    }
-
-    @Override
-    public R rightOrElse(final R fallback) {
-      return this.value;
-    }
-
     @Override
     public <T> T unwrap(final Function<L, T> onLeft, final Function<R, T> onRight) {
       return onRight.apply(this.value);