Merge pull request xyzsd#3 from fdelsert/empty_instance

Empty Singleton

src/main/java/net/xyzsd/dichotomy/Empty.java

@@ -7,8 +7,18 @@
  * as it cannot be instantiated, and extensive null-checking is in place.
  * </p>
  * <p>
- * Instead, the {@link Empty} type can be used. All {@link Empty} types are considered equivalent.
+ * Instead, the {@link Empty} type can be used.
  * </p>
  */
-public record Empty() {}
+public final class Empty {
+
+ private static Empty INSTANCE = new Empty();
+
+ private Empty() {
+ }
+
+ public static Empty getInstance() {
+ return INSTANCE;
+ }
+}
 // 'Empty' instead of None to differ from Maybe.None. 'Nil' could be a consideration. or maybe all caps to denote singleton ('NONE')

src/main/java/net/xyzsd/dichotomy/Result.java

@@ -97,7 +97,7 @@ static <V, E> Result<V, E> ofOK(@NotNull V value) {
  */
  @NotNull
  static <E> Result<Empty, E> ofOK() {
- return new OK<>( new Empty() );
+ return new OK<>( Empty.getInstance() );
  }
 
  /**
@@ -123,7 +123,7 @@ static <E> Result<Empty, E> ofOK() {
  */
  @NotNull
  static <V> Result<V, Empty> ofNullable(@Nullable V value) {
- return (value == null) ? ofErr( new Empty() ) : ofOK( value );
+ return (value == null) ? ofErr( Empty.getInstance() ) : ofOK( value );
  }
 
  /**
@@ -152,7 +152,7 @@ static <V> Result<V, Empty> ofNullable(@Nullable V value) {
  @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
  @NotNull
  static <V> Result<V, Empty> from(@NotNull Optional<V> opt) {
- return opt.<Result<V, Empty>>map( Result::ofOK ).orElseGet( () -> Result.ofErr( new Empty() ) );
+ return opt.<Result<V, Empty>>map( Result::ofOK ).orElseGet( () -> Result.ofErr( Empty.getInstance() ) );
  }
 
  /**

src/main/java/net/xyzsd/dichotomy/trying/Try.java

@@ -54,7 +54,7 @@ static <V, E extends Exception> Try<V, E> ofOK(@NotNull V value) {
  */
  @NotNull
  static <E extends Exception> Try<Empty, E> ofOK() {
- return new OK<>( new Empty() );
+ return new OK<>( Empty.getInstance() );
  }
 
  /**

src/test/java/net/xyzsd/dichotomy/EmptyTest.java

@@ -0,0 +1,19 @@
+package net.xyzsd.dichotomy;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class EmptyTest {
+
+ @Test
+ void uniqueness() {
+ assertSame(Empty.getInstance(), Empty.getInstance());
+ }
+
+ @Test
+ void equality() {
+ assertEquals(Empty.getInstance(), Empty.getInstance());
+ }
+
+}

src/test/java/net/xyzsd/dichotomy/ResultTest.java

@@ -56,7 +56,7 @@ void ofOK() {
  void ofOK_NONE() {
  final Result<Empty, Object> result = Result.ofOK();
  assertEquals( OK.class, result.getClass() );
- assertEquals( new Empty(), ((OK<Empty, Object>) result).get() );
+ assertEquals( Empty.getInstance(), ((OK<Empty, Object>) result).get() );
  }
 
  @Test

src/test/java/net/xyzsd/dichotomy/trying/TryTest.java

@@ -187,7 +187,7 @@ void ofOK() {
  void ofOK_NONE() {
  final Try<Empty, RuntimeException> result = Try.ofOK();
  assertEquals( Try.OK.class, result.getClass() );
- assertEquals( new Empty(), ((Try.OK<Empty, RuntimeException>) result).get() );
+ assertEquals( Empty.getInstance(), ((Try.OK<Empty, RuntimeException>) result).get() );
  }