.NET (Core and Framework)

Public Class MirrorObservableCollection(Of T)
    Inherits ObservableCollection(Of T)

    Friend Sub New(ByVal base As IList(Of T), ByVal mirror As Func(Of T, T))
    End Sub
End Class

Public NotInheritable Class MirrorObservableCollection
    Private Sub New()
    End Sub

    Public Shared Function Create(Of TItem, _
                                     TList As {INotifyCollectionChanged, _
                                               IList(Of TItem)})( _
                              ByVal base As TList, _
                              ByVal mirror As Func(Of TItem, TItem))  _
                       As MirrorObservableCollection(Of TItem)
        Return New MirrorObservableCollection(Of TItem)(base, mirror)
    End Function
End Class

Dim mirror = Function(s As String) s.ToUpperInvariant()
Dim base = New ObservableCollection(Of String)()
'this works
Dim m1 = MirrorObservableCollection.Create(Of String, _
             ObservableCollection(Of String))(base, mirror)
'this is what I want to do
'Compile Error: Data type of the type parameters in method 
'Create cannot be inferred from these arguments
Dim m2 = MirrorObservableCollection.Create(base, mirror)

Dim asFunc As Func(Of String, String) = Function(s) s.ToUpperInvariant()
Dim m3 = MirrorObservableCollection.Create(base, asFunc)
Dim m4 = MirrorObservableCollection.Create(base, Function(s As String) s.ToUpperInvariant())
'This does not work, the compiler cannot infer the lambda parameter type.
Dim m5 = MirrorObservableCollection.Create(base, Function(s) s.ToUpperInvariant())