Unhandled Exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
This is documented as:
InvalidOperationException is used in cases when the failure to invoke a method is caused by reasons other than invalid arguments. For example, InvalidOperationException is thrown by:
MoveNext if objects of a collection are modified after the enumerator is created.
Argh, sometimes enumerators are just too conservative. This seems to be the case:
Hashtable hashTable = new Hashtable();
foreach (object key in hashTable.Keys)
hashTable[key] = "something else";
To solve this, all we have to do is to get another collection to iterate:
foreach (object key in new ArrayList(hashTable.Keys))
Though understanding this behavior, the responsibility of this sanity check could probably be delegated optionally to the programmer. In my sample I am not changing the enumeration, just the value. Lets not forget that the new ArrayList solution depends upon memory usage.