From 8e2e2cbe63fd7cf7a30e76d5693e47aa0c427f31 Mon Sep 17 00:00:00 2001
From: Glavo <zjx001202@gmail.com>
Date: Mon, 23 Oct 2023 02:44:23 +0800
Subject: [PATCH] Close #71: Create Either::bifold

---
 .../src/main/java/kala/control/Either.java    | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/kala-base/src/main/java/kala/control/Either.java b/kala-base/src/main/java/kala/control/Either.java
index ce600e2c..873a81ae 100644
--- a/kala-base/src/main/java/kala/control/Either.java
+++ b/kala-base/src/main/java/kala/control/Either.java
@@ -9,6 +9,7 @@
 import java.io.Serializable;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -78,6 +79,13 @@ public abstract <U> U fold(
             @NotNull Function<? super B, ? extends U> rightMapper
     );
 
+    public abstract <C, D, U> U bifold(
+            @NotNull Either<? extends C, ? extends D> other,
+            U defaultValue,
+            @NotNull BiFunction<? super A, ? super C, ? extends U> leftMapper,
+            @NotNull BiFunction<? super B, ? super D, ? extends U> rightMapper
+    );
+
     @Contract("-> new")
     public abstract @NotNull Either<B, A> swap();
 
@@ -190,6 +198,20 @@ public <U> U fold(
             return leftMapper.apply(value);
         }
 
+        @Override
+        public <C, D, U> U bifold(
+                @NotNull Either<? extends C, ? extends D> other,
+                U defaultValue,
+                @NotNull BiFunction<? super A, ? super C, ? extends U> leftMapper,
+                @NotNull BiFunction<? super B, ? super D, ? extends U> rightMapper) {
+
+            if (other instanceof Left) {
+                return leftMapper.apply(this.value, ((Left<? extends C, ? extends D>) other).value);
+            } else {
+                return defaultValue;
+            }
+        }
+
         /**
          * {@inheritDoc}
          */
@@ -332,6 +354,20 @@ public <U> U fold(
             return rightMapper.apply(value);
         }
 
+        @Override
+        public <C, D, U> U bifold(
+                @NotNull Either<? extends C, ? extends D> other,
+                U defaultValue,
+                @NotNull BiFunction<? super A, ? super C, ? extends U> leftMapper,
+                @NotNull BiFunction<? super B, ? super D, ? extends U> rightMapper) {
+
+            if (other instanceof Right) {
+                return rightMapper.apply(this.value, ((Right<? extends C, ? extends D>) other).value);
+            } else {
+                return defaultValue;
+            }
+        }
+
         /**
          * {@inheritDoc}
          */