Update iterator pattern examples

Author: nemanjarogic

src/BehavioralPatterns/Iterator/IteratorLibrary/ConceptualExample/Collections/Common/IterableCollection.cs

@@ -5,4 +5,4 @@ namespace IteratorLibrary.ConceptualExample.Collections.Common;
 public abstract class IterableCollection : IEnumerable
 {
     public abstract IEnumerator GetEnumerator();
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/ConceptualExample/Collections/WordsCollection.cs

@@ -6,34 +6,19 @@ namespace IteratorLibrary.ConceptualExample.Collections;
 
 public class WordsCollection : IterableCollection
 {
-    private readonly List<string> _collection = new List<string>();
-    private bool _isDirectionReversed = false;
+    private readonly List<string> _collection = new();
+    private bool _isDirectionReversed;
 
-    public int Count
-    {
-        get
-        {
-            return _collection.Count;
-        }
-    }
+    public int Count => _collection.Count;
 
-    public void Add(string word)
-    {
-        _collection.Add(word);
-    }
+    public void Add(string word) => _collection.Add(word);
 
-    public List<string> GetItems()
-    {
-        return _collection;
-    }
+    public void ReverseDirection() => _isDirectionReversed = !_isDirectionReversed;
 
-    public void ReverseDirection()
-    {
-        _isDirectionReversed = !_isDirectionReversed;
-    }
+    public override IEnumerator GetEnumerator() => new AlphabeticalOrderIterator(this, _isDirectionReversed);
 
-    public override IEnumerator GetEnumerator()
-    {
-        return new AlphabeticalOrderIterator(this, _isDirectionReversed);
-    }
-}
+    public string this[int index] =>
+        index >= 0 && index < _collection.Count
+            ? _collection[index]
+            : throw new ArgumentOutOfRangeException(nameof(index));
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/ConceptualExample/ConceptualExecutor.cs

@@ -1,4 +1,5 @@
-using BuildingBlocks;
+using System.Collections;
+using BuildingBlocks;
 using IteratorLibrary.ConceptualExample.Collections;
 
 namespace IteratorLibrary.ConceptualExample;
@@ -19,18 +20,25 @@ public static void Execute()
         };
 
         Console.WriteLine("Straight traversal:");
-
         foreach (var item in collection)
         {
             Console.WriteLine(item);
         }
 
         Console.WriteLine("\nReverse traversal:");
         collection.ReverseDirection();
-
         foreach (var item in collection)
         {
             Console.WriteLine(item);
         }
+
+        // It is also possible to pass an iterator to a client class instead of giving it access to a whole collection.
+        // This way, you don't expose the collection to the client at all.
+        Console.WriteLine("\nReverse traversal using alternative approach:");
+        IEnumerator enumerator = collection.GetEnumerator();
+        while (enumerator.MoveNext())
+        {
+            Console.WriteLine(enumerator.Current);
+        }
     }
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/ConceptualExample/Iterators/AlphabeticalOrderIterator.cs

@@ -10,14 +10,14 @@ namespace IteratorLibrary.ConceptualExample.Iterators;
 public class AlphabeticalOrderIterator : Iterator
 {
     /// <summary>
-    /// Stores the current traversal position. An iterator may have a lot of
-    /// other fields for storing iteration state, especially when it is
-    /// supposed to work with a particular kind of collection.
+    /// Stores the current traversal position.
+    /// An iterator may have a lot of other fields for storing iteration state,
+    /// especially when it is supposed to work with a particular kind of collection.
     /// </summary>
     private int _position = -1;
 
     private readonly WordsCollection _collection;
-    private readonly bool _isDirectionReversed = false;
+    private readonly bool _isDirectionReversed;
 
     public AlphabeticalOrderIterator(WordsCollection collection, bool isDirectionReversed = false)
     {
@@ -30,14 +30,11 @@ public AlphabeticalOrderIterator(WordsCollection collection, bool isDirectionRev
         }
     }
 
-    public override object Current()
-    {
-        return _collection.GetItems()[_position];
-    }
+    public override object Current() => _collection[_position];
 
     public override bool MoveNext()
     {
-        int updatedPosition = _position + (_isDirectionReversed ? -1 : 1);
+        var updatedPosition = _position + (_isDirectionReversed ? -1 : 1);
 
         if (updatedPosition >= 0 && updatedPosition < _collection.Count)
         {
@@ -48,8 +45,5 @@ public override bool MoveNext()
         return false;
     }
 
-    public override void Reset()
-    {
-        _position = _isDirectionReversed ? _collection.Count : -1;
-    }
-}
+    public override void Reset() => _position = _isDirectionReversed ? _collection.Count : -1;
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/ConceptualExample/Iterators/Common/Iterator.cs

@@ -7,8 +7,6 @@ public abstract class Iterator : IEnumerator
     object IEnumerator.Current => Current();
 
     public abstract object Current();
-
     public abstract bool MoveNext();
-
     public abstract void Reset();
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/Executor.cs

@@ -13,4 +13,4 @@ public override void Execute()
         ConceptualExecutor.Execute();
         MusicFestivalsExecutor.Execute();
     }
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/MusicFestivalsExample/Collections/Common/IIterableCollection.cs

@@ -5,4 +5,4 @@ namespace IteratorLibrary.MusicFestivalsExample.Collections.Common;
 public interface IIterableCollection
 {
     IIterator CreateIterator();
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/MusicFestivalsExample/Collections/FestivalCollection.cs

@@ -6,25 +6,13 @@ namespace IteratorLibrary.MusicFestivalsExample.Collections;
 
 public class FestivalCollection : IIterableCollection
 {
-    private readonly List<MusicFestival> _festivals = new List<MusicFestival>();
+    private readonly List<MusicFestival> _festivals = new();
 
-    public int Count
-    {
-        get { return _festivals.Count; }
-    }
+    public int Count => _festivals.Count;
 
-    public void Add(MusicFestival festival)
-    {
-        _festivals.Add(festival);
-    }
+    public void Add(MusicFestival festival) => _festivals.Add(festival);
 
-    public MusicFestival Get(int index)
-    {
-        return _festivals[index];
-    }
+    public MusicFestival Get(int index) => _festivals[index];
 
-    public IIterator CreateIterator()
-    {
-        return new FestivalIterator(this);
-    }
-}
+    public IIterator CreateIterator() => new FestivalIterator(this);
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/MusicFestivalsExample/Iterators/Common/IIterator.cs

@@ -5,10 +5,7 @@ public interface IIterator
     int Step { get; set; }
 
     MusicFestival First();
-
     MusicFestival Current();
-
     bool MoveNext();
-
     void Reset();
-}
+}

src/BehavioralPatterns/Iterator/IteratorLibrary/MusicFestivalsExample/Iterators/FestivalIterator.cs

@@ -16,14 +16,18 @@ public FestivalIterator(FestivalCollection collection)
         _step = 1;
     }
 
+    // It's probably more logical to have a method for changing the step.
+    // However, for demo purposes the idea was to show that iterator interface can contain properties too.
     public int Step
     {
-        get
-        {
-            return _step;
-        }
+        get => _step;
         set
         {
+            if (value <= 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(value), "The step can be only positive value. The current iterator doesn't support going backward.");
+            }
+
             _step = value;
         }
     }
@@ -34,14 +38,11 @@ public MusicFestival First()
         return Current();
     }
 
-    public MusicFestival Current()
-    {
-        return _collection.Get(_position);
-    }
+    public MusicFestival Current() => _collection.Get(_position);
 
     public bool MoveNext()
     {
-        int updatedPosition = _position + _step;
+        var updatedPosition = _position + _step;
 
         if (updatedPosition < _collection.Count)
         {
@@ -52,8 +53,5 @@ public bool MoveNext()
         return false;
     }
 
-    public void Reset()
-    {
-        _position = -1;
-    }
-}
+    public void Reset() => _position = -1;
+}