1 public sealed class ReserseEnumerable<T> : IEnumerable<T>
2 {
3 private class ReserseEnumerator : IEnumerator<T>
4 {
5 int currentIndex;
6 IList<T> collection;
7 public ReserseEnumerator(IList<T> srcCollection)
8 {
9 collection = srcCollection;
10 currentIndex = collection.Count;
11 }
12
13 #region IEnumerator<T> Members
14
15 public T Current
16 {
17 get { return collection[currentIndex]; }
18 }
19
20 #endregion
21
22 #region IDisposable Members
23
24 public void Dispose()
25 {
26
27 }
28
29 #endregion
30
31 #region IEnumerator Members
32
33 object IEnumerator.Current
34 {
35 get { return this.Current; }
36 }
37
38 public bool MoveNext()
39 {
40 return --currentIndex >= 0;
41 }
42
43 public void Reset()
44 {
45 currentIndex = collection.Count;
46 }
47
48 #endregion
49 }
50
51 IEnumerable<T> sourceSequence;
52 public IList<T> originalSequence;
53
54 public ReserseEnumerable(IEnumerable<T> sequence)
55 {
56 sourceSequence = sequence;
57 }
58 #region IEnumerable<T> Members
59
60 public IEnumerator<T> GetEnumerator()
61 {
62 if (originalSequence == null)
63 {
64 originalSequence = new List<T>();
65 foreach (T item in sourceSequence)
66 {
67 originalSequence.Add(item);
68 }
69 }
70 return new ReserseEnumerator(originalSequence);
71 }
72
73 #endregion
74
75 #region IEnumerable Members
76
77 IEnumerator System.Collections.IEnumerable.GetEnumerator()
78 {
79 return this.GetEnumerator();
80 }
81
82 #endregion
83 }

1 public ReverseEnumerable(IEnumerable<T> sequence)
2 {
3 sourceSequence = sequence;
4 // If sequence doesn't implement IList<T>,
5 // originalSequence is null, so this works
6 // fine.
7 originalSequence = sequence as IList<T>;
8 }
9
10 public ReverseEnumerable(IList<T> sequence)
11 {
12 sourceSequence = sequence;
13 originalSequence = sequence;
14 }

1 public IEnumerator<T> GetEnumerator()
2 {
3 // Create a copy of the original sequence,
4 // so it can be reversed.
5 if (originalSequence == null)
6 {
7 if (sourceSequence is ICollection<T>)
8 {
9 ICollection<T> source = sourceSequence
10 as ICollection<T>;
11 originalSequence = new List<T>(source.Count);
12 }
13 else
14 originalSequence = new List<T>();
15 foreach (T item in sourceSequence)
16 originalSequence.Add(item);
17 }
18 return new ReverseEnumerator(originalSequence);
19 }