Performance Enum vs class? - vb.net

Question

i found few new style (for me) to "define" output from select query.
Private Enum Item
ID
Item
Description
End Enum
Private Class Item
Private ID as String
Private Item as String
Private Desc as String
End Class
I 'm thinking of using either one of them. by using class i does not need to re-cast the element type before i display. but Enum seems like easier to understand.
Anyone have some suggestion how to decide?

Answer 1

Enum members are numeric (usually integer, but can be long). But they are not variable and do not change at runtime. So your enum equates to:
Private Enum Item
ID = 0
Item = 1
Description = 2
End Enum
If you want Description to be a string, then a class is a better idea. Enums are used to reference or index something or limit/define a selection. Like:
Public Property Stooge As Stooges
Friend Enum Stooges
Larry
Moe
Curly
Shemp
CurlyJoe
End Enum
The Stooge Property must be one of those values. in code it will show you the text ("moe") but store and integer (1). users will be shown the text in drop downs etc.
You can associate a description with Enum constants:
Public Enum Stooges
<Description("Larry - Funny one")> Larry
<Description("Moe - 'Smart' One")> Moe
<Description("Curly - Sore One")> Curly
<Description("Shemp - One with bad haircut")> Shemp
<Description("CurlyJoe - Last one")> CurlyJoe
End Enum
To get the description for a single one:
Public Shared Function GetDescription(ByVal EnumConstant As [Enum]) As String
Dim fi As Reflection.FieldInfo =
EnumConstant.GetType().GetField(EnumConstant.ToString())
Dim attr() As DescriptionAttribute =
DirectCast(fi.GetCustomAttributes(GetType(DescriptionAttribute),
False), DescriptionAttribute())
If attr.Length > 0 Then
Return attr(0).Description
Else
Return EnumConstant.ToString() ' return enum name if no Descr
End If
End Function
Usage: str = enumHelper.GetDescription(Stooge.Moe) (enumHelper is the name of the calss where the static/shared function resides).
To get a String Array of all the descriptions:
Public Shared Function GetDescriptions(ByVal type As Type) As String()
Dim n As Integer = 0
Dim enumValues As Array
Try
enumValues = [Enum].GetValues(type)
Dim Descr(enumValues.Length - 1) As String
For Each value As [Enum] In enumValues
Descr(n) = GetDescription(value)
n += 1
Next
Return Descr
Catch ex As Exception
MessageBox.Show(ex.Message)
Return Nothing
End Try
End Function
Usage: Dim strEnum As String() = enumHelper.GetDescriptions(GetType(Stooges))

Answer 2

From your question, what you really mean is Struct vs Class. I would default to creating a class. The main reason to use a struct vs a class, is when you need value semantics -- assignment/parameters copies the bits, not a pointer. This is fairly rare in my experience. Unless you have a compelling reason (and you know the difference), go with a class.