[Mono-bugs] [Bug 27713][Wis] New - Enumerator Collection with the use of pattern matching

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Changed by mwh@sysrq.dk.

http://bugzilla.ximian.com/show_bug.cgi?id=27713

--- shadow/27713	Fri Jul 12 11:22:36 2002
+++ shadow/27713.tmp.9566	Fri Jul 12 11:22:36 2002
@@ -0,0 +1,136 @@
+Bug#: 27713
+Product: Mono/Runtime
+Version: unspecified
+OS: other
+OS Details: LFS
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Wishlist
+Component: misc
+AssignedTo: mono-bugs@ximian.com                            
+ReportedBy: mwh@sysrq.dk               
+QAContact: mono-bugs@ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: Enumerator Collection with the use of pattern matching
+
+Description of Problem:
+I just followed a nice c# book on how to implement a Enumerator Collection
+without using the Interface approch, the program compiles, but does not run.
+
+
+Steps to reproduce the problem:
+Here is the program:
+using System;
+using System.Collections;
+
+class Foobar {
+	public static void Main() {
+		IntList list = new IntList();
+		list.Add (1);
+		list.Add (55);
+		list.Add (43);
+		
+		foreach (int val in list)
+			Console.WriteLine ("Value = {0}", val);
+	}
+}
+
+class IntList {
+	int[] values = new int[10];
+	int allocated = 10;
+	int count = 0;
+	int revision = 0;
+
+	public void Add (int value) {
+		if (count+1 == allocated) {
+			int[] newValues = new int[allocated*=2];
+			for (int i = 0; i < count; i++) {
+				newValues[i] = values[i];
+			}
+			values = newValues;
+		}
+
+		values[count] = value;
+		count++;
+		revision++;
+	}
+
+	public int Count {
+		get { return count;}
+	}
+
+	void CheckIndex (int index) {
+		if (index >= count || index < 0)
+			throw new ArgumentOutOfRangeException ("Index      value out of range");
+	}
+
+	public int this[int index] {
+		get {
+			CheckIndex (index);
+			return values[index];
+		} set {
+			CheckIndex (index);
+			values[index] = value;
+			revision++;
+		}
+	}
+
+	public IntListEnumerator GetEnumerator() {
+		return new IntListEnumerator (this);
+	}
+
+	internal int Revision {
+		get { return revision; }
+	}
+}
+
+class IntListEnumerator {
+	IntList intList;
+	int revision;
+	int index;
+
+	internal IntListEnumerator (IntList intList) {
+		this.intList = intList;
+		Reset();
+	}
+
+	public bool MoveNext() {
+		return ++index >= intList.Count ? false : true;
+	}
+
+	public int Current {
+		get {
+			if (revision != intList.Revision) {
+				throw new InvalidOperationException 
+					("Collection modified while enumerating");
+			}
+			return intList[index];
+		}
+	}
+
+	public void Reset() {
+		index = -1;
+		revision = intList.Revision;
+	}
+}
+
+Actual Results:
+WARNING **: unhandled exception System.NullReferenceException: "A null
+value was found where an object instance was required"
+in <0x000cb> .Foobar:Main ()
+
+Expected Results: 
+Value = 1
+Value = 55
+Value = 43
+RESULT: 0
+
+How often does this happen? 
+Everytime.
+
+Additional Information:
+Compiled/Ran with mono 0.12
+It compiled and Ran under MS winblows .. Dick /#mono tried it.