Add "contains" method to Collection.

lib/core/collection.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
- * The [Collection] interface is the public interface of all
- * collections.
+ * The common interface of all collections.
+ *
+ * The [Collection] class contains a skeleton implementation of
+ * an iterator based collection.
  */
 abstract class Collection<E> extends Iterable<E> {
   /**
-   * Applies the function [f] to each element of this collection.
-   */
-  void forEach(void f(E element));
-
-  /**
    * Returns a new collection with the elements [: f(e) :]
    * for each element [:e:] of this collection.
    *
-   * Note on typing: the return type of f() could be an arbitrary
-   * type and consequently the returned collection's
-   * typeis Collection.
+   * Subclasses of [Collection] should implement the [map] method
+   * to return a collection of the same general type as themselves.
+   * E.g., [List.map] should return a [List].
    */
   Collection map(f(E element));
 
   /**
+   * Returns a collection with the elements of this collection
+   * that satisfy the predicate [f].
+   *
+   * The returned collection should be of the same type as the collection
+   * creating it.
+   *
+   * An element satisfies the predicate [f] if [:f(element):]
+   * returns true.
+   */
+  Collection<E> filter(bool f(E element));
+
+  /**
+   * Returns the number of elements in this collection.
+   */
+  int get length;
+
+  /**
+   * Check whether the collection contains an element equal to [element].
+   */
+  bool contains(E element) {
+    for (E e in this) {
+      if (e == element) return true;
+    }
+    return false;
+  }
+
+  /**
+   * Applies the function [f] to each element of this collection.
+   */
+  void forEach(void f(E element)) {
+    for (E element in this) f(element);
+  }
+
+  /**
    * Reduce a collection to a single value by iteratively combining each element
    * of the collection with an existing value using the provided function.
    * Use [initialValue] as the initial value, and the function [combine] to
    * create a new value from the previous one and an element.
    *
    * Example of calculating the sum of a collection:
    *
    *   collection.reduce(0, (prev, element) => prev + element);
    */
-  Dynamic reduce(Dynamic initialValue,
-                 Dynamic combine(Dynamic previousValue, E element));
-
-  /**
-   * Returns a new collection with the elements of this collection
-   * that satisfy the predicate [f].
-   *
-   * An element satisfies the predicate [f] if [:f(element):]
-   * returns true.
-   */
-  Collection<E> filter(bool f(E element));
+  Dynamic reduce(var initialValue,

[ngeoffray, 2012/10/16 15:08:18]

Why is this one 'var'?

[sra1, 2012/10/16 18:52:52]

I thought the standard coding style was to leave out Dynamic where possible.

reduce(initValue, combine(previousValue, E element)) {

[Lasse Reichstein Nielsen, 2012/10/17 11:06:45]

I'm not sure it's *standard*, but it's definitely one of the opposing views :)
I prefer always writing a type to make the code more readable and show that the
dynamic typing is deliberate, and leave untyped code to quick hacks (and it's
great that we support that too!).
In this case, some Dynamic's could be written as the shorter "var" instead, but
return types can't.

+                 Dynamic combine(var previousValue, E element)) {

[ngeoffray, 2012/10/16 15:08:18]

ditto

+    var value = initialValue;

[ngeoffray, 2012/10/16 15:08:18]

Why this?

[sra1, 2012/10/16 18:52:52]

It would be wrong to overwrite 'initialValue' since then the name 'initialValue'
would be misleading.

[Lasse Reichstein Nielsen, 2012/10/17 11:06:45]

Exactly :)

+    for (Element element in this) value = combine(value, element);

[ngeoffray, 2012/10/16 15:08:18]

Element -> E

[Lasse Reichstein Nielsen, 2012/10/17 11:06:45]

Thanks.

+    return value;
+  }
 
   /**
    * Returns true if every elements of this collection satisify the
    * predicate [f]. Returns false otherwise.
    */
-  bool every(bool f(E element));
+  bool every(bool f(E element)) {
+    for (E element in this) {
+      if (!f(element)) return false;
+    }
+    return true;
+  }
 
   /**
    * Returns true if one element of this collection satisfies the
    * predicate [f]. Returns false otherwise.
    */
-  bool some(bool f(E element));
+  bool some(bool f(E element)) {
+    for (E element in this) {
+      if (f(element)) return true;
+    }
+    return false;
+  }
 
   /**
    * Returns true if there is no element in this collection.
    */
-  bool isEmpty();
-
-  /**
-   * Returns the number of elements in this collection.
-   */
-  int get length;
+  bool isEmpty() => !iterator().hasNext();
 }