Public Function TryGetFirst( _
   ByRef item As KeyValuePair(Of TKey,TValue) _
) As Boolean

public bool TryGetFirst( 
   out KeyValuePair<TKey,TValue> item
)

BTreeDictionary<int, string> data = new BTreeDictionary<int, string>();
data.Add(1, "a");
data.Add(2, "b");
data.Add(3, "c");
data.Add(4, "d");
data.Add(5, "e");

Assert.AreEqual(1, data.First().Key);
Assert.AreEqual("a", data.First().Value);
data.Remove(1);
Assert.AreEqual(2, data.First().Key);
Assert.AreEqual("b", data.First().Value);

Assert.AreEqual(5, data.Last().Key);
Assert.AreEqual("e", data.Last().Value);
data.Remove(5);
Assert.AreEqual(4, data.Last().Key);
Assert.AreEqual("d", data.Last().Value);

data.Remove(4);
data.Remove(3);

KeyValuePair<int, string> kv;
Assert.IsTrue(data.TryGetLast(out kv));
Assert.IsTrue(data.TryGetFirst(out kv));
data.Remove(2);
Assert.IsFalse(data.TryGetLast(out kv));
Assert.IsFalse(data.TryGetFirst(out kv));

try
{
    data.First();
    Assert.Fail("Should raise InvalidOperationException");
}
catch (InvalidOperationException)
{
}
try
{
    data.Last();
    Assert.Fail("Should raise InvalidOperationException");
}
catch (InvalidOperationException)
{
}

Dim data As New BTreeDictionary(Of Integer, String)()
data.Add(1, "a")
data.Add(2, "b")
data.Add(3, "c")
data.Add(4, "d")
data.Add(5, "e")

Assert.AreEqual(1, data.First().Key)
Assert.AreEqual("a", data.First().Value)
data.Remove(1)
Assert.AreEqual(2, data.First().Key)
Assert.AreEqual("b", data.First().Value)

Assert.AreEqual(5, data.Last().Key)
Assert.AreEqual("e", data.Last().Value)
data.Remove(5)
Assert.AreEqual(4, data.Last().Key)
Assert.AreEqual("d", data.Last().Value)

data.Remove(4)
data.Remove(3)

Dim kv As KeyValuePair(Of Integer, String)
Assert.IsTrue(data.TryGetLast(kv))
Assert.IsTrue(data.TryGetFirst(kv))
data.Remove(2)
Assert.IsFalse(data.TryGetLast(kv))
Assert.IsFalse(data.TryGetFirst(kv))

Try
    data.First()
    Assert.Fail("Should raise InvalidOperationException")
Catch generatedExceptionName As InvalidOperationException
End Try
Try
    data.Last()
    Assert.Fail("Should raise InvalidOperationException")
Catch generatedExceptionName As InvalidOperationException
End Try