feature: #1842 Add Currying Design Pattern (#2271)

* #1842 Setting up project and creating example classes. Issues running site and deploy * #1842 Added unit tests * #1842 Improved example * #1842 Added UML class diagram * #1842 Added comments to Genre class * #1842 Improved readability of lambda function * #1842 Started working on the README and created initial UML * #1842 Added example to README * #1842 Replaced prints with LOGGER * #1842 Fixed typo in README * #1842 Testing commit account * #1842 Adding documentation to App class * #1842 Improved documentation * #1842 Added documentation to AppTest * #1842 Fixing latex formating issue * #1842 Improving the intent description * #1842 Removed override methods from the UML diagram for clarity * #1842 Renamed the SCI_FI enum * #1842 Updated the currying pom.xml * #1842 Removed unneeded comment * #1842 Improving documentation and README * Added review changes. * Fixing build issues and added javadoc comments to functional interfaces. * Removing code smells * Removed unnecessary toString method * Using lombok to reduce boiler plate. * Fixed frontmatter. * Removing function name code smell * Fixed README typo * Added book_creator test to improve coverage Co-authored-by: Hugo Kat <u7286091@anu.edu.au>
2026-08-05 12:23:29 +00:00 · 2022-12-04 11:48:57 +02:00
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+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.currying;
+
+import java.time.LocalDate;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+* Currying decomposes a function with multiple arguments in multiple functions that
+* take a single argument. A curried function which has only been passed some of its
+* arguments is called a partial application. Partial application is useful since it can
+* be used to create specialised functions in a concise way.
+*
+* <p>In this example, a librarian uses a curried book builder function create books belonging to
+* desired genres and written by specific authors.
+*/
+@Slf4j
+public class App {
+  /**
+  * Main entry point of the program.
+  */
+  public static void main(String[] args) {
+    LOGGER.info("Librarian begins their work.");
+
+    // Defining genre book functions
+    Book.AddAuthor fantasyBookFunc = Book.builder().withGenre(Genre.FANTASY);
+    Book.AddAuthor horrorBookFunc = Book.builder().withGenre(Genre.HORROR);
+    Book.AddAuthor scifiBookFunc = Book.builder().withGenre(Genre.SCIFI);
+
+    // Defining author book functions
+    Book.AddTitle kingFantasyBooksFunc = fantasyBookFunc.withAuthor("Stephen King");
+    Book.AddTitle kingHorrorBooksFunc = horrorBookFunc.withAuthor("Stephen King");
+    Book.AddTitle rowlingFantasyBooksFunc = fantasyBookFunc.withAuthor("J.K. Rowling");
+
+    // Creates books by Stephen King (horror and fantasy genres)
+    Book shining = kingHorrorBooksFunc.withTitle("The Shining")
+            .withPublicationDate(LocalDate.of(1977, 1, 28));
+    Book darkTower = kingFantasyBooksFunc.withTitle("The Dark Tower: Gunslinger")
+            .withPublicationDate(LocalDate.of(1982, 6, 10));
+
+    // Creates fantasy books by J.K. Rowling
+    Book chamberOfSecrets = rowlingFantasyBooksFunc.withTitle("Harry Potter and the Chamber of Secrets")
+            .withPublicationDate(LocalDate.of(1998, 7, 2));
+
+    // Create sci-fi books
+    Book dune = scifiBookFunc.withAuthor("Frank Herbert")
+            .withTitle("Dune")
+            .withPublicationDate(LocalDate.of(1965, 8, 1));
+    Book foundation = scifiBookFunc.withAuthor("Isaac Asimov")
+            .withTitle("Foundation")
+            .withPublicationDate(LocalDate.of(1942, 5, 1));
+
+    LOGGER.info("Stephen King Books:");
+    LOGGER.info(shining.toString());
+    LOGGER.info(darkTower.toString());
+
+    LOGGER.info("J.K. Rowling Books:");
+    LOGGER.info(chamberOfSecrets.toString());
+
+    LOGGER.info("Sci-fi Books:");
+    LOGGER.info(dune.toString());
+    LOGGER.info(foundation.toString());
+  }
+}
@@ -0,0 +1,117 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.currying;
+
+import java.time.LocalDate;
+import java.util.Objects;
+import java.util.function.Function;
+import lombok.AllArgsConstructor;
+
+/**
+ * Book class.
+ */
+@AllArgsConstructor
+public class Book {
+  private final Genre genre;
+  private final String author;
+  private final String title;
+  private final LocalDate publicationDate;
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    Book book = (Book) o;
+    return Objects.equals(author, book.author)
+            && Objects.equals(genre, book.genre)
+            && Objects.equals(title, book.title)
+            && Objects.equals(publicationDate, book.publicationDate);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(author, genre, title, publicationDate);
+  }
+
+  @Override
+  public String toString() {
+    return "Book{" + "genre=" + genre + ", author='" + author + '\''
+            + ", title='" + title + '\'' + ", publicationDate=" + publicationDate + '}';
+  }
+
+  /**
+   * Curried book builder/creator function.
+   */
+  static Function<Genre, Function<String, Function<String, Function<LocalDate, Book>>>> book_creator
+      = bookGenre
+          -> bookAuthor
+              -> bookTitle
+                  -> bookPublicationDate
+                      -> new Book(bookGenre, bookAuthor, bookTitle, bookPublicationDate);
+
+  /**
+   * Implements the builder pattern using functional interfaces to create a more readable book
+   * creator function. This function is equivalent to the BOOK_CREATOR function.
+   */
+  public static AddGenre builder() {
+    return genre
+        -> author
+            -> title
+                -> publicationDate
+                    -> new Book(genre, author, title, publicationDate);
+  }
+
+  /**
+   * Functional interface which adds the genre to a book.
+   */
+  public interface AddGenre {
+    Book.AddAuthor withGenre(Genre genre);
+  }
+
+  /**
+   * Functional interface which adds the author to a book.
+   */
+  public interface AddAuthor {
+    Book.AddTitle withAuthor(String author);
+  }
+
+  /**
+   * Functional interface which adds the title to a book.
+   */
+  public interface AddTitle {
+    Book.AddPublicationDate withTitle(String title);
+  }
+
+  /**
+   * Functional interface which adds the publication date to a book.
+   */
+  public interface AddPublicationDate {
+    Book withPublicationDate(LocalDate publicationDate);
+  }
+}
@@ -0,0 +1,34 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.currying;
+
+/**
+ * Enum representing different book genres.
+ */
+public enum Genre {
+  FANTASY,
+  HORROR,
+  SCIFI;
+}
@@ -0,0 +1,39 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.currying;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that the App can be run without throwing any exceptions.
+ */
+class AppTest {
+  @Test
+  void executesWithoutExceptions() {
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+  }
+}
@@ -0,0 +1,83 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.currying;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+
+/**
+ * Unit tests for the Book class
+ */
+class BookCurryingTest {
+  private static Book expectedBook;
+
+  @BeforeAll
+  public static void initialiseBook() {
+    expectedBook = new Book(Genre.FANTASY,
+        "Dave",
+        "Into the Night",
+        LocalDate.of(2002, 4, 7));
+  }
+
+  /**
+   * Tests that the expected book can be created via curried functions
+   */
+  @Test
+  void createsExpectedBook() {
+    Book builderCurriedBook = Book.builder()
+        .withGenre(Genre.FANTASY)
+        .withAuthor("Dave")
+        .withTitle("Into the Night")
+        .withPublicationDate(LocalDate.of(2002, 4, 7));
+
+    Book funcCurriedBook = Book.book_creator
+            .apply(Genre.FANTASY)
+            .apply("Dave")
+            .apply("Into the Night")
+            .apply(LocalDate.of(2002, 4, 7));
+
+    assertEquals(expectedBook, builderCurriedBook);
+    assertEquals(expectedBook, funcCurriedBook);
+  }
+
+  /**
+   * Tests that an intermediate curried function can be used to create the expected book
+   */
+  @Test
+  void functionCreatesExpectedBook() {
+    Book.AddTitle daveFantasyBookFunc = Book.builder()
+      .withGenre(Genre.FANTASY)
+      .withAuthor("Dave");
+
+    Book curriedBook = daveFantasyBookFunc.withTitle("Into the Night")
+      .withPublicationDate(LocalDate.of(2002, 4, 7));
+
+    assertEquals(expectedBook, curriedBook);
+  }
+}