const vs. 方法参数的枚举

Question

I have a seemingly very basic question. I'm trying to decide whether or not constants strings would really be better than enums with MyEnum.ToString() called for a high performance application.

I have a class, enum, method like this...

    Public Enum MyEnum
        MyValue1
        MyValue2
    End Enum

    Public Class MyImportantClass

            Public Sub Foo(ByVal enumerationValue As MyEnum)

            ' Some code in here that needs to do this at some point
            Dim str As String = enumerationValue.ToString()

    End Sub

    End Class

I understand enumerationValue.ToString() has some performance issues. However, another developer suggested instead of using Enums, use Constant Strings. My problem is that the method parameter is then a string, and the caller can then pass whatever he wants. Not just any string will work, obviously, so this is a run-time bug.

Public Sub Foo(ByVal enumerationValue As String)

    ' Some code in here that needs to do this at some point
    '   Dim str As String = enumerationValue

End Sub

I want the safety of the enum, but the performance of a constant. As I said, I'm looking for a way to have my cake and eat it too.

Answer 1

Enum is by far the way to go. Somewhat self-documenting and definately falling into the 'pit of success' becuase you'll never get bogus data.

I don't know for sure but I would suspect .ToString() does nice stuff - don't worry about it. It gets called a lot!

Answer 2

OK, this may not be what you want, but it provides for type safety and prevents you from having to do a ToString later. First set up a class w/ one property that doesn't have a setter, and a New method that does the setting:

Public Class MyEnumObj
    Private _Value As String
    Public ReadOnly Property Value As String
        Get
            Return _Value
        End Get
    End Property
    Private Sub New()
        ' Hide the default constructor '
    End Sub
    Public Sub New(inValue As String)
        _Value = inValue
    End Sub
End Class

Then declare your "constants":

Public MyValue1 As New MyEnumObj("MyValue1")
Public MyValue2 As New MyEnumObj("MyValue2")

They're not constant but can't be modified, and I think by proper use of Friend you can arrange it so nobody else can create the objects, either. Now you can say:

Public Sub Foo(Optional ByVal enumerationValue As MyEnumObj = Nothing)

        ' Some code in here that needs to do this at some point '
        Dim str As String = If(enumerationValue IsNot Nothing, enumerationValue.Value, String.Empty)

End Sub

This may be overkill, but objects do tend to lend themselves to type safety.

Answer 3

Stick with enum, it's a lot more user frendly with passing as a parameter to a function. The IDE can pop-up the list of available items.

To convert your enum to string, you could have a dictionnary of (Enum, String)

or

There's some nice articles on how to put attributes on your enum, this way you can convert it to a string.

Can I give an enum an attribute in VB.NET (like I can do in Java)?

http://weblogs.asp.net/stefansedich/archive/2008/03/12/enum-with-string-values-in-c.aspx