Public Overloads Shared Function Merge( _
   ByVal comparer As IComparer(Of TKey), _
   ByVal duplicateHandling As DuplicateHandling, _
   ByVal ParamArray enums() As IEnumerable(Of KeyValuePair(Of TKey,TValue)) _
) As IEnumerable(Of KeyValuePair(Of TKey,TValue))

public static IEnumerable<KeyValuePair<TKey,TValue>> Merge( 
   IComparer<TKey> comparer,
   DuplicateHandling duplicateHandling,
   params IEnumerable<KeyValuePair<TKey,TValue>>[] enums
)

var x = new[] { new KeyValuePair<int, int>(1, 1) };
var y = new[] { new KeyValuePair<int, int>(1, 2), new KeyValuePair<int, int>(2, 2) };

IEnumerator<KeyValuePair<int, int>> e =
    OrderedKeyValuePairs<int, int>
    .Merge(Comparer<int>.Default, DuplicateHandling.FirstValueWins, x, y)
    .GetEnumerator();

Assert.IsTrue(e.MoveNext());
Assert.AreEqual(1, e.Current.Key);
Assert.AreEqual(1, e.Current.Value);
Assert.IsTrue(e.MoveNext());
Assert.AreEqual(2, e.Current.Key);
Assert.AreEqual(2, e.Current.Value);
Assert.IsFalse(e.MoveNext());
            
e = OrderedKeyValuePairs<int, int>
    .Merge(Comparer<int>.Default, DuplicateHandling.LastValueWins, x, y)
    .GetEnumerator();

Assert.IsTrue(e.MoveNext());
Assert.AreEqual(1, e.Current.Key);
Assert.AreEqual(2, e.Current.Value);
Assert.IsTrue(e.MoveNext());
Assert.AreEqual(2, e.Current.Key);
Assert.AreEqual(2, e.Current.Value);
Assert.IsFalse(e.MoveNext());

Dim x As var = New () {New KeyValuePair(Of Integer, Integer)(1, 1)}
Dim y As var = New () {New KeyValuePair(Of Integer, Integer)(1, 2), New KeyValuePair(Of Integer, Integer)(2, 2)}

Dim e As IEnumerator(Of KeyValuePair(Of Integer, Integer)) = OrderedKeyValuePairs(Of Integer, Integer).Merge(Comparer(Of Integer).[Default], DuplicateHandling.FirstValueWins, x, y).GetEnumerator()

Assert.IsTrue(e.MoveNext())
Assert.AreEqual(1, e.Current.Key)
Assert.AreEqual(1, e.Current.Value)
Assert.IsTrue(e.MoveNext())
Assert.AreEqual(2, e.Current.Key)
Assert.AreEqual(2, e.Current.Value)
Assert.IsFalse(e.MoveNext())

e = OrderedKeyValuePairs(Of Integer, Integer).Merge(Comparer(Of Integer).[Default], DuplicateHandling.LastValueWins, x, y).GetEnumerator()

Assert.IsTrue(e.MoveNext())
Assert.AreEqual(1, e.Current.Key)
Assert.AreEqual(2, e.Current.Value)
Assert.IsTrue(e.MoveNext())
Assert.AreEqual(2, e.Current.Key)
Assert.AreEqual(2, e.Current.Value)
Assert.IsFalse(e.MoveNext())