mcs/class/corlib/System/CharEnumerator.cs

   1 //
   2 // System.CharEnumerator.cs
   3 //
   4 // Author: Duncan Mak  (duncan@ximian.com)
   5 //
   6 // (C) Ximian, Inc.
   7 //
   8
   9 using System.Collections;
  10
  11 namespace System
  12 {
  13         [Serializable]
  14         public sealed class CharEnumerator : IEnumerator, ICloneable
  15         {
  16                 private string str;
  17                 private int index;
  18                 private int length;
  19                 // Representation invariant:
  20                 // length == str.Length
  21                 // -1 <= index <= length
  22
  23                 // Constructor
  24                 internal CharEnumerator (string s)
  25                 {
  26                          str = s;
  27                          index = -1;
  28                          length = s.Length;
  29                 }
  30
  31                 // Property
  32                 public char Current
  33                 {
  34                         get {
  35                                 if (index == -1 || index == length)
  36                                         throw new InvalidOperationException
  37                                                 ("The position is not valid.");
  38
  39                                 return str [index];
  40                         }
  41                 }
  42
  43                 object IEnumerator.Current
  44                 {
  45                         get {
  46                                 if (index == -1 || index == length)
  47                                         throw new InvalidOperationException
  48                                                 ("The position is not valid");
  49
  50                                 return str [index];
  51                         }
  52                 }
  53
  54                 // Methods
  55                 public object Clone ()
  56                 {
  57                         CharEnumerator x = new CharEnumerator (str);
  58                         x.index = index;
  59                         return x;
  60                 }
  61
  62                 public bool MoveNext ()
  63                 {
  64                         // Representation invariant holds: -1 <= index <= length
  65
  66                         index ++;
  67
  68                         // Now: 0 <= index <= length+1;
  69                         //   <=>
  70                         // 0 <= index < length (OK) ||
  71                         // length <= index <= length+1 (Out of bounds)
  72
  73                         if (index >= length) {
  74                                 index = length;
  75                                 // Invariant restored:
  76                                 // length == index
  77                                 //   =>
  78                                 // -1 <= index <= length
  79                                 return false;
  80                         }
  81                         else
  82                                 return true;
  83                 }
  84
  85                 public void Reset ()
  86                 {
  87                         index = -1;
  88                 }
  89         }
  90 }