Question

I have an Enum thus:

Enum CurrentPeriodType
   CurrentDate
   Sales
   Utilization
End Enum

I have a function thus:

Private Sub PopulateDDLPeriods(currentPeriodType As CurrentPeriodType)

...

End Sub

I make a function call thus:

PopulateDDLPeriods(False)

I run it, it compiles and runs, and I step through the code and indeed it is going from the function call into the function that expects an ENUM. I thought maybe I had an overload…but I actually stepped through the code and it went into the ENUM parameter-typed function…

HUH?

Answer 1

This is only possible because your Option Strict is off. If you do not like the behavior that you see, turn it on. However, doing so will also imply Option Explicit forcing you to declare all variables, and also to specify the data type of your Enum which is how we knew you had it off.

In your case, the internal value of CurrentDate is 0. It is therefore not very surprising (considering that Option Strict is off) that False can convert to 0 and also to the enum.

What could be more surprising is that your code will compile and run even after you change it as follows:

Enum CurrentPeriodType
   CurrentDate = 1
   Sales = 2
   Utilization = 3
End Enum

or alternatively, if you start passing in True (which converts to -1).

As you can see, .NET enums are just “partly enumerated” synonyms for their respective underlying data types and you can get in any value of such a data type if you try just a little.