Why is this an issue?
Flags enumerations should not rely on the language to initialize the values of their members. Implicit initialization will set the first member to
0, and increment the value by one for each subsequent member. This implicit behavior does not allow members to be combined using the bitwise or
operator in a useful way.
Instead, 0 and powers of two (i.e. 1, 2, 4, 8, 16, …) should be used to explicitly initialize all the members.
Noncompliant code example
<Flags()>
Enum FruitType ' Non-Compliant
None
Banana
Orange
Strawberry
End Enum
Module Module1
Sub Main()
Dim bananaAndStrawberry = FruitType.Banana Or FruitType.Strawberry
' Will display only Strawberry!
Console.WriteLine(bananaAndStrawberry.ToString())
End Sub
End Module
Compliant solution
<Flags()>
Enum FruitType ' Compliant
None = 0
Banana = 1
Orange = 2
Strawberry = 4
End Enum
Module Module1
Sub Main()
Dim bananaAndStrawberry = FruitType.Banana Or FruitType.Strawberry
' Will display Banana and Strawberry, as expected.
Console.WriteLine(bananaAndStrawberry.ToString())
End Sub
End Module
Exceptions
The default initialization of 0, 1, 2, 3, 4, … matches 0, 1, 2, 4, 8 … in the first three values, so no issue is reported if the first three
members of the enumeration is not initialized.
