Cast generic structure to other structure - vb.net

Question

I'm having trouble wrapping my head around the problem I'm having. I want to apply some general rules to structures, and as the type of them differs, I want to use a generic function to do this. My problem is that to manipulate the structure via methods only available with parameters of a specified type, I can not find a way to do so without extensive casting. See, for example, what steps are needed to specify that a DateTime value should always be specified as UTC:
Public Shared Function Sanitize(Of T As Structure)(retValue As T?) As T?
' If value is DateTime it must be specified as UTC:
If GetType(T) = GetType(DateTime) AndAlso retVal.HasValue Then
' To specify the value as UTC, it must first be casted into DateTime, as it is not know to the compiler that the type in fact IS
' DateTime, even if we just checked.
Dim retValAsObj = CType(retVal, Object)
Dim retValAsObjAsDateTime = CType(retValAsObj, DateTime)
Dim retValWithSpecifiedKind = DateTime.SpecifyKind(retValAsObjAsDateTime, DateTimeKind.Utc)
retVal = CType(CType(retValWithSpecifiedKind, Object), T?)
End If
Return retVal
End Function
Am I missing something? Casting four times for such a simple task seems to complex for me to be the best / simplest solution.

Answer 1

You can use extension methods
With extension method you don't need to check type and cast it.
With extension method you will have own method for every type - simple to maintain
With extension method you will have "readable" syntax
<Extension>
Public Shared Function Sanitize(Date? nullable) AS Date?
{
If nullable.HasValue = False Then Return nullable
Return DateTime.SpecifyKind(nullable.Value, DateTimeKind.Utc)
}
<Extension>
Public Shared Function Sanitize(Integer? nullable) AS Integer?
{
If nullable.HasValue = False Then Return nullable
If nullable.Value < 0 Then Return 0
Return nullable.Value
}
Somewhere in the code
Dim sanitizedDate As Date? = receivedDate.Sanitize()
Dim sanitizedAmount As Integer? = receivedAmount.Sanitize()
Extension methods have some downsides - for example you not able to "mock" them for unit testing, which force you to test "Sanitize" method every time it used (if you are using Test-First approach).