Add Iterator (ES5 + ES6 + CoffeeScript + TypeScript)

Author: Badacadabra

doc/GoF/Behavioral/Iterator/Iterator.dia

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+# Synopsis
+
+I am at the library and I would like to see the list of all available books.
+
+# Problem
+
+There is generally a huge amount of books in a library, so it is great to have a catalog that allows you to have a quick overview of all available references. This catalog may be a bit special and could contain a one-page presentation for each book.
+
+In Javascript, we could use a simple loop to get the list of all books. But in fact, this would not be so convenient because each data structure and entity may have its own particularities when it comes to iteration. For instance, we know we cannot iterate through an array literal like we iterate through an object literal (array-like objects could be considered as an exception). Therefore this is generally a good idea to simplify the work to iterate through a collection...
+
+# Solution
+
+Iterator is the design pattern we need for this. To implement this pattern, we could have:
+
+  * An abstract representation of a collection (abstract class or interface)
+  * An abstract representation of a catalog (abstract class or interface)
+  * A concrete collection like a library (which is a collection of books)
+  * A concrete catalog like a library catalog (which references all books)
+
+In this particular case, a collection is an iterable object whereas a catalog is an iterator object.

doc/GoF/Behavioral/Iterator/Iterator.png

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+# ==============================
+# ABSTRACT ITERATOR 
+# ==============================
+
+class Catalog
+    constructor: ->
+        throw new Error "You cannot instantiate an abstract class!" if @constructor is Catalog 
+
+    hasNext: ->
+        throw new Error "You cannot call an abstract method!"
+
+    next: ->
+        throw new Error "You cannot call an abstract method!"
+
+# ==============================
+# ABSTRACT ITERABLE 
+# ==============================
+
+class Collection
+    constructor: ->
+        throw new Error "You cannot instantiate an abstract class!" if @constructor is Collection
+
+    list: ->
+        throw new Error "You cannot call an abstract method!"
+
+# ==============================
+# CONCRETE ITERATOR 
+# ==============================
+
+class LibraryCatalog extends Catalog
+    constructor: (@_collection) ->
+        @_index = 0
+
+    hasNext: ->
+        @_index < @_collection.getBooks().length
+
+    next: ->
+        @_collection.getBooks()[@_index++]
+
+# ==============================
+# CONCRETE ITERABLE 
+# ==============================
+
+class Library extends Collection 
+    constructor: (@_books) ->
+
+    list: ->
+        new LibraryCatalog(@)
+
+    getBooks: ->
+        @_books
+
+# ==============================
+# CLIENT CODE
+# ==============================
+
+# We get the iterator (catalog) from the iterable object (library)
+library = new Library ["Foo", "Bar"]
+catalog = library.list()
+
+console.log catalog.next() while catalog.hasNext()

doc/GoF/Behavioral/Iterator/README.md

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+// ==============================
+// ABSTRACT ITERATOR 
+// ==============================
+
+interface Catalog {
+    hasNext(): boolean; 
+    next(): string;
+}
+
+// ==============================
+// ABSTRACT ITERABLE 
+// ==============================
+
+interface Collection {
+    list(): Catalog;
+}
+
+// ==============================
+// CONCRETE ITERATOR 
+// ==============================
+
+class LibraryCatalog implements Catalog {
+    private index: number = 0;
+    private collection: Library; 
+
+    constructor(collection: Library) {
+        this.collection = collection;
+    }
+
+    hasNext(): boolean {
+        return this.index < this.collection.getBooks().length;
+    }
+
+    next(): string {
+        return this.collection.getBooks()[this.index++];
+    }
+}
+
+// ==============================
+// CONCRETE ITERABLE 
+// ==============================
+
+class Library implements Collection {
+    private books: string[];
+
+    constructor(books: string[]) {
+        this.books = books;
+    }
+
+    public list(): LibraryCatalog {
+        return new LibraryCatalog(this);
+    }
+
+    public getBooks(): string[] {
+        return this.books; 
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+// We get the iterator (catalog) from the iterable object (library)
+let library: Library = new Library(["Foo", "Bar"]),
+    catalog: LibraryCatalog = library.list();
+
+while (catalog.hasNext()) {
+    console.log(catalog.next());
+}

src/CoffeeScript/GoF/Behavioral/Iterator/Iterator.coffee

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+'use strict';
+
+// ==============================
+// ABSTRACT ITERATOR 
+// ==============================
+
+var Catalog = (function () {
+    function Catalog() {
+        if (this.constructor === Catalog) {
+            throw new Error("You cannot instantiate an abstract class!");
+        } 
+    }
+
+    Catalog.prototype.hasNext = function () {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    Catalog.prototype.next = function () {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    return Catalog;
+})(); 
+
+// ==============================
+// ABSTRACT ITERABLE 
+// ==============================
+
+var Collection = (function () {
+    function Collection() {
+        if (this.constructor === Collection) {
+            throw new Error("You cannot instantiate an abstract class!");
+        } 
+    }
+
+    Collection.prototype.list = function() {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    return Collection;
+})();
+
+// ==============================
+// CONCRETE ITERATOR 
+// ==============================
+
+var LibraryCatalog = (function () {
+    var index = 0;
+
+    function LibraryCatalog(collection) {
+        this._collection = collection;
+    }
+    LibraryCatalog.prototype = Object.create(Catalog.prototype);
+    LibraryCatalog.prototype.constructor = LibraryCatalog;
+
+    LibraryCatalog.prototype.hasNext = function () {
+        return index < this._collection.getBooks().length;
+    };
+
+    LibraryCatalog.prototype.next = function () {
+        return this._collection.getBooks()[index++];
+    };
+
+    return LibraryCatalog;
+})();
+
+// ==============================
+// CONCRETE ITERABLE 
+// ==============================
+
+var Library = (function () {
+    var books = [];
+
+    function Library(refs) {
+        books = refs;
+    }
+    Library.prototype = Object.create(Collection.prototype);
+    Library.prototype.constructor = Library;
+
+    Library.prototype.list = function () {
+        return new LibraryCatalog(this);
+    };
+
+    Library.prototype.getBooks = function () {
+        return books; 
+    };
+
+    return Library;
+})();
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+// We get the iterator (catalog) from the iterable object (library)
+var library = new Library(["Foo", "Bar"]),
+    catalog = library.list();
+
+while (catalog.hasNext()) {
+    console.log(catalog.next());
+}

src/TypeScript/GoF/Behavioral/Iterator/Iterator.ts

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+// ==============================
+// ABSTRACT ITERATOR 
+// ==============================
+
+class Catalog {
+    constructor() {
+        if (new.target !== undefined) {
+            throw new Error("You cannot instantiate an abstract class!");
+        } 
+    }
+
+    hasNext() {
+        throw new Error("You cannot call an abstract method!");
+    }
+
+    next() {
+        throw new Error("You cannot call an abstract method!");
+    }
+}
+
+// ==============================
+// ABSTRACT ITERABLE 
+// ==============================
+
+class Collection {
+    constructor() {
+        if (new.target !== undefined) {
+            throw new Error("You cannot instantiate an abstract class!");
+        } 
+    }
+
+    list() {
+        throw new Error("You cannot call an abstract method!");
+    }
+}
+
+// ==============================
+// CONCRETE ITERATOR 
+// ==============================
+
+class LibraryCatalog extends Catalog {
+    constructor(collection) {
+        super();
+        this._index = 0;
+        this._collection = collection;
+    }
+
+    hasNext() {
+        return this._index < this._collection.books.length;
+    }
+
+    next() {
+        return this._collection.books[this._index++];
+    }
+}
+
+// ==============================
+// CONCRETE ITERABLE 
+// ==============================
+
+class Library extends Collection {
+    constructor(books) {
+        super();
+        this._books = books;
+    }
+
+    list() {
+        return new LibraryCatalog(this);
+    }
+
+    get books() {
+        return this._books; 
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+// We get the iterator (catalog) from the iterable object (library)
+let library = new Library(["Foo", "Bar"]),
+    catalog = library.list();
+
+while (catalog.hasNext()) {
+    console.log(catalog.next());
+}