[Mono-bugs] [Bug 572084] New: HashSet<T>.SymmetricExceptWith assumes argument contains no duplicate items

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http://bugzilla.novell.com/show_bug.cgi?id=572084

http://bugzilla.novell.com/show_bug.cgi?id=572084#c0


           Summary: HashSet<T>.SymmetricExceptWith assumes argument
                    contains no duplicate items
    Classification: Mono
           Product: Mono: Class Libraries
           Version: 2.4.x
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Sys.Core
        AssignedTo: jbevain at novell.com
        ReportedBy: cdhowie at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


Created an attachment (id=337540)
 --> (http://bugzilla.novell.com/attachment.cgi?id=337540)
Test case

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.7)
Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)

HashSet<T>.SymmetricExceptWith assumes that the IEnumerable<T> argument does
not contain any duplicate items, and so it behaves differently than MS.NET.  If
the enumerable does contain duplicate items, it is acted on twice.  So if an
enumerable is passed with only two items, and they are equal, the set will not
change since the item will be added once and removed once (not necessarily in
that order).

Reproducible: Always

Steps to Reproduce:
1. Create a HastSet<T>.
2. Create an IEnumerable<T> containing two equal elements.
3. Call HashSet<T>.SymmetricExceptWith using this enumerable.
Actual Results:  
The set contents are not different following the operation.

Expected Results:  
The set should now contain the element in the enumerable if it did not
previously, and should not contain the element if it did previously.

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