2002-09-13 Nick Drochak <ndrochak@gol.com>

[mono.git] / mcs / class / corlib / System / CharEnumerator.cs

diff --git a/mcs/class/corlib/System/CharEnumerator.cs b/mcs/class/corlib/System/CharEnumerator.cs
index b36d567ad8ae6d156c102e7cadc14e53dc89e859..7689a5a3b4ce1e2386295460c20c910dee636d9e 100644 (file)
--- a/mcs/class/corlib/System/CharEnumerator.cs
+++ b/mcs/class/corlib/System/CharEnumerator.cs
@@ -16,6 +16,9 @@ namespace System
                private string str;
                private int index;
                private int length;
+               // Representation invariant:
+               // length == str.Length
+               // -1 <= index <= length
                
                // Constructor
                internal CharEnumerator (string s)
@@ -29,7 +32,7 @@ namespace System
                public char Current
                {
                        get {
-                               if (index == -1)
+                               if (index == -1 || index == length)
                                        throw new InvalidOperationException
                                                ("The position is not valid.");
 
@@ -40,7 +43,7 @@ namespace System
                object IEnumerator.Current
                {
                        get {
-                               if (index == -1)
+                               if (index == -1 || index == length)
                                        throw new InvalidOperationException
                                                ("The position is not valid");
 
@@ -58,13 +61,23 @@ namespace System
                
                public bool MoveNext ()
                {
-                       if (length == 0)
-                               return false;                   
+                       // Representation invariant holds: -1 <= index <= length
 
                        index ++;
+
+                       // Now: 0 <= index <= length+1;
+                       //   <=>
+                       // 0 <= index < length (OK) || 
+                       // length <= index <= length+1 (Out of bounds)
                        
-                       if (index == length)                            
-                               return false;
+                       if (index >= length) {
+                               index = length;
+                               // Invariant restored:
+                               // length == index
+                               //   =>
+                               // -1 <= index <= length
+                               return false;   
+                       }
                        else
                                return true;
                }