Implementing Multiple Interfaces

[akiaz]

I have a question regarding implementing multiple interfaces in vb.net versus c#. This code works good in c#:

interface IDatabaseUser
{
    void LookupPassword();
}
interface ITestUser
{
    void LookupPassword();
}
public class testcode : IDatabaseUser, ITestUser
{
    public void LookupPassword()
    {
        //
    }
    void ITestUser.LookupPassword()
    {
        //
    }
}

but the "equivalent" code (so I think) in vb.net:

Public Interface IDatabaseUser
    Sub LookupPassword()
End Interface
Public Interface ITestUser
    Sub LookupPassword()
End Interface
Public Class User
    Implements IDatabaseUser, ITestUser
    Public Sub LookupPassword()
        '
    End Sub
    Public Sub LookupPassword() Implements ITestUser.LookupPassword
        '
    End Sub

gives an error stating that I must implement 'Sub LookupPassword()', so when I change the method declaration to

Public Sub LookupPassword() Implements IDatabaseUser.LookupPassword

I still get the same error, but now I also get an error:

'LookupPassword' cannot implement 'LookupPassword' because there is no matching sub on interface 'IDatabaseUser'

Is there a fundamental difference in implementing multiple interfaces between c# and vb.net or am I doing something wrong here that is simple to correct?

 

[akiaz]

Also, in the vb.net code, I get the error:

Method 'LookupPassword' has multiple definitions with identical signatures.

Which I do not get in c#. I thought they have to be the same when specifying the interface that is implemented for the method otherwise this makes no sense.

 

[PlausiblyDamp]

Public Interface IDatabaseUser

	Sub LookupPassword()

End Interface

Public Interface ITestUser

	Sub LookupPassword()

End Interface

Public Class User

	Implements IDatabaseUser, ITestUser

	Public Sub LookupPassword2() Implements IDatabaseUser.LookupPassword

		'

	End Sub

	Public Sub LookupPassword() Implements ITestUser.LookupPassword

		'

	End Sub
End Class

 

[akiaz]

I see. So when I create a User object and then make a reference to it like this:

Dim guy As New User
Dim dbguy As IDatabaseUser = guy

I use b.LookupPassword and not b.LookupPassword2. Actually, now I'm curious as to why vb.net is this way and c# is not. Is there some other limitation or advantage in doing interfaces like this between languages?

 

[akiaz]

oo limitation?

VB is a dog!

lol , well it's actually kinda annoying more than anything but I can sort of get around it by naming class members like this instead:

Public Sub LookupPassword_DatabaseUser Implements IDatabaseUser.LookupPassword
' and
Public Sub LookupPassword_TestUser Implements ITestUser.LookupPassword

but that makes the lines long which is why I prefer the c# method. Doesn't really matter though to me as long as they both work the same. Where I work, our coders use vb.net and/or c# so that's why it's important they work the same.

An alternate thing that I found that I do not like is that when an interface inherits from another interface, the implementing class can only have one member that implements the base interface member (sounds like a tongue twister ). So I can't do something like this:

Interface IStandardUser
    Sub LookupPassword()
End Interface
Interface IDatabaseUser
    Inherits IStandardUser
End Interface
Interface ITestUser
    Inherits IStandardUser
End Interface
Public Class User
    Implements IDatabaseUser, ITestUser
    Public Sub LookupPassword_DatabaseUser() Implements IDatabaseUser.LookupPassword
        '
    End Sub
    Public Sub LookupPassword_TestUser() Implements ITestUser.LookupPassword
        '
    End Sub
End Class

Because I get the error:
'IStandardUser.LookupPassword' cannot be implemented more than once.

So I cannot have a base interface, and the same is true for c#. I wonder if this is a .NET limitation (or design standard) or if this is pretty much standard across other object oriented languages. Or maybe my approach is alltogether wrong