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

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

using (BPlusTree<int, string> data = Create(Options))
{
    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) { }
}

Using data As BPlusTree(Of Integer, String) = Create(Options)
    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
End Using