RE: passing enum value as an argument

Madestro <me_no_like_spam_juanDOTromero@bowneDOTcom> wrote:
> Once again, please read the posts above. I did talk about Option Strict.

You mentioned it in an earlier post, but not in the post which
specifically said that a call to TakeFirstEnum(SecondEnum.Fred)
succeeds. You didn't even mention it in the post before that. How was
anyone supposed to work out that you were talking about the (hopefully
unusual) situation of working with Option Strict off in a post made 16
hours after your only previous reference to Option Strict?

> I clearly stated that you could CAST to the Enum type. Obviously IMPLICIT
> conversions will yield an error with Option Strict ON, that is the whole
> point of it.

Indeed.

> As for the evaluation at runtime, because the compiler knows the type, a
> constant or variable would provide THE SAME level of type safety.

No it wouldn't - because unless you declare a new type for each
constant (in which case you've basically got an enum anyway) you would
have to use the same type (eg Int32) for different types of constant,
at which point you *have* lost type safety.

In your first post in the thread, you said:

<quote>
That would defeat the purpose of having an Enum. you might as well
create three variables then.
</quote>

What type would you make those variables have?

> The range of values IS part of the safety. If you don't believe me, read the
> documentation and/or attempt to assign an integer outside of the range and
> you will see what happens. E.g.:
>
> Enum Juan
> Zero 'By default this is initialized to 0
> One 'By default this is initialized to 1
> Two 'By default this is initialized to 2
> End Enum
>
> Public sub New()
> Test(2) ------------> Option Strict OFF, this will be OK
> Test(3) ------------> Option Strict OFF, this will FAIL
> Test(ctype(2,Juan)) ------------> Option Strict ON, This will be OK
> Test(ctype(3,Juan)) -------------> Option Strict ON, this will FAIL
> End Sub

Unlike you, I've actually tried the code. Compile and run the
following:

Option Strict On

Imports System

Public Enum FirstEnum
Foo
Bar
Baz
End Enum

Public Class Test

Shared Sub TakeFirstEnum (value As FirstEnum)
Console.WriteLine (value)
End Sub

Shared Sub Main()
TakeFirstEnum(CType(5, FirstEnum))
End Sub
End Class

Compile it from the command line:
vbc Test.vb
Run it:
5

I think you'll agree that 5 is outside the range of the enum, and yet
it works. How do you explain that?

> As you can see I am not *entirely* wrong. Try creating another Enum and pass
> it to the function (with casting if using Option Strict ON) and you will see
> that the value is accepted so long as it is in the range of the enum.

No, it's accepted whether or not it's in the range of the enum.

> As far as ambiguity, a language can NEVER allow you to use the name
> directly. Consider the following scenario:
>
> Public Class One
> Dim Juan as integer = 0
> Enum Sample
> Juan = 1
> Javier = 2
> End Enum
> Public Sub New()
> console.writeline(Juan) --------> * This will print "1"
> End Sub
> End Class
>
> How will the compiler resolve this variable?

It can't. So in this case, the compiler would force you to
disambiguate. That doesn't mean there aren't many, many cases where
there *isn't* any ambiguity, and where the compiler could infer the
type.

<snip>

> Finally, I never post anything until I try it myself.

Please explain how the code which you claim won't work works perfectly
fine then.

By the way, your test code also fails to compile because you haven't
declared the return type of your Test function, and because the enum
you declared was called "Juan" but you declared the parameter to the
function to be of type "JuanEnum". Here's your code tidied up. It
doesn't fail where you claimed it would, by the way.

Option Strict On

Imports System

Public Enum Juan
Zero 'By default this is initialized to 0
One 'By default this is initialized to 1
Two 'By default this is initialized to 2
End Enum


Public Class Foo

Public Shared Sub Test(ByVal e as Juan)
End Sub


Shared Sub Main()
Test(ctype(2,Juan))
Test(ctype(3,Juan))
End Sub
End Class


--
Jon Skeet - <skeet@xxxxxxxxx>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
.

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