Public Delegate Function KeyValueUpdate
    (Of TKey,TValue)( _
   ByVal key As TKey, _
   ByVal original As TValue _
) As TValue

public delegate TValue KeyValueUpdate<TKey,TValue>( 
   TKey key,
   TValue original
)

SynchronizedDictionary<int, string> data =
    new SynchronizedDictionary<int, string>(new Dictionary<int, string>());

Assert.IsTrue(data.TryAdd(1, "a"));
Assert.IsFalse(data.TryAdd(1, "a"));

Assert.IsTrue(data.TryUpdate(1, "a"));
Assert.IsTrue(data.TryUpdate(1, "c"));
Assert.IsTrue(data.TryUpdate(1, "d", "c"));
Assert.IsFalse(data.TryUpdate(1, "f", "c"));
Assert.AreEqual("d", data[1]);
Assert.IsTrue(data.TryUpdate(1, "a", data[1]));
Assert.AreEqual("a", data[1]);
Assert.IsFalse(data.TryUpdate(2, "b"));

string val;
Assert.IsTrue(data.TryRemove(1, out val) && val == "a");
Assert.IsFalse(data.TryRemove(2, out val));
Assert.AreNotEqual(val, "a");

Assert.IsFalse(data.TryUpdate(1, (k, x) => x.ToUpper()));
data[1] = "a";
data[1] = "b";
Assert.IsTrue(data.TryUpdate(1, (k, x) => x.ToUpper()));
Assert.AreEqual("B", data[1]);

Dim data As New SynchronizedDictionary(Of Integer, String)(New Dictionary(Of Integer, String)())

Assert.IsTrue(data.TryAdd(1, "a"))
Assert.IsFalse(data.TryAdd(1, "a"))

Assert.IsTrue(data.TryUpdate(1, "a"))
Assert.IsTrue(data.TryUpdate(1, "c"))
Assert.IsTrue(data.TryUpdate(1, "d", "c"))
Assert.IsFalse(data.TryUpdate(1, "f", "c"))
Assert.AreEqual("d", data(1))
Assert.IsTrue(data.TryUpdate(1, "a", data(1)))
Assert.AreEqual("a", data(1))
Assert.IsFalse(data.TryUpdate(2, "b"))

Dim val As String
Assert.IsTrue(data.TryRemove(1, val) AndAlso val = "a")
Assert.IsFalse(data.TryRemove(2, val))
Assert.AreNotEqual(val, "a")

Assert.IsFalse(data.TryUpdate(1, Function(k, x) x.ToUpper()))
data(1) = "a"
data(1) = "b"
Assert.IsTrue(data.TryUpdate(1, Function(k, x) x.ToUpper()))
Assert.AreEqual("B", data(1))