VB equivelant for C#'s default(T)

[=?Utf-8?B?Y291Z2FyaXN0aWM=?=]

I am trying to convert an C# application to VB and have one issue which is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate this in
VB.Net

Thanks

[=?Utf-8?B?RGF2aWQgQW50b24=?=]

'Nothing'.
This keyword is more general than the C# 'null', handling reference types,
value types, and generic types.
--
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"cougaristic" wrote:

I am trying to convert an C# application to VB and have one issue which is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate this in
VB.Net

Thanks

[Mythran]

"David Anton" <Da********@discussions.microsoft.comwrote in message
news:BD**********************************@microsof t.com...

'Nothing'.
This keyword is more general than the C# 'null', handling reference types,
value types, and generic types.
--
http://www.tangiblesoftwaresolutions.com
C++ to C#
C++ to VB
C++ to Java
VB & C# to Java
Java to VB & C#
Instant C#: VB to C#
Instant VB: C# to VB
Instant C++: VB, C#, or Java to C++/CLI
"cougaristic" wrote:

>I am trying to convert an C# application to VB and have one issue which
is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate this
in
VB.Net

Thanks

From what I've read, default(T) just gets the default value of the type.
So, in Visual Basic, as David Anton explains before me, the value of
"Nothing" should accomplish this same goal (reference types have a reference
to null (or Nothing in VB.Net) by default. Value types, when you set them
to Nothing, will be set to their default types (although, I think you
shouldn't be able to set a value type to Nothing....but that's just my
opinion :D ).

HTH,
Mythran

[=?Utf-8?B?Y291Z2FyaXN0aWM=?=]

Just to learn more about this situation I would like to know how to handle
the following to return the 'actual' default for the generic type used.

When I am using Guid as the generic value like the following:
GetMessageHeader(Of Guid)(message,name,ns) it currently returns nothing if
the else statement is reached? Wouldn't the default of a guid be a guid type
containing all zeros?

Here is the converted code in question:

Public Shared Function GetMessageHeader(Of T)(ByVal message As Message,
ByVal name As String, ByVal ns As String) As T
Dim index As Integer = message.Headers.FindHeader(name, ns)
If (index -1) Then
Dim val As T = message.Headers.GetHeader(Of T)(name, ns)
Return val
Else
'The following is what this question is all about
'C# = default(T)
Return Nothing
End If
End Function

Thanks

"Mythran" wrote:

>

"David Anton" <Da********@discussions.microsoft.comwrote in message
news:BD**********************************@microsof t.com...

'Nothing'.
This keyword is more general than the C# 'null', handling reference types,
value types, and generic types.
--
http://www.tangiblesoftwaresolutions.com
C++ to C#
C++ to VB
C++ to Java
VB & C# to Java
Java to VB & C#
Instant C#: VB to C#
Instant VB: C# to VB
Instant C++: VB, C#, or Java to C++/CLI
"cougaristic" wrote:

I am trying to convert an C# application to VB and have one issue which
is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate this
in
VB.Net

Thanks

From what I've read, default(T) just gets the default value of the type.
So, in Visual Basic, as David Anton explains before me, the value of
"Nothing" should accomplish this same goal (reference types have a reference
to null (or Nothing in VB.Net) by default. Value types, when you set them
to Nothing, will be set to their default types (although, I think you
shouldn't be able to set a value type to Nothing....but that's just my
opinion :D ).

HTH,
Mythran

[=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=]

cougaristic,

Isn't a guid an integer? Then assigning Nothing to it will result in the
default value for an integer, which is all zeroes.

Kerry Moorman
"cougaristic" wrote:

Just to learn more about this situation I would like to know how to handle
the following to return the 'actual' default for the generic type used.

When I am using Guid as the generic value like the following:
GetMessageHeader(Of Guid)(message,name,ns) it currently returns nothing if
the else statement is reached? Wouldn't the default of a guid be a guid type
containing all zeros?

Here is the converted code in question:

Public Shared Function GetMessageHeader(Of T)(ByVal message As Message,
ByVal name As String, ByVal ns As String) As T
Dim index As Integer = message.Headers.FindHeader(name, ns)
If (index -1) Then
Dim val As T = message.Headers.GetHeader(Of T)(name, ns)
Return val
Else
'The following is what this question is all about
'C# = default(T)
Return Nothing
End If
End Function

Thanks

"Mythran" wrote:

"David Anton" <Da********@discussions.microsoft.comwrote in message
news:BD**********************************@microsof t.com...

'Nothing'.
This keyword is more general than the C# 'null', handling reference types,
value types, and generic types.
--
http://www.tangiblesoftwaresolutions.com
C++ to C#
C++ to VB
C++ to Java
VB & C# to Java
Java to VB & C#
Instant C#: VB to C#
Instant VB: C# to VB
Instant C++: VB, C#, or Java to C++/CLI
>
>
"cougaristic" wrote:
>
>I am trying to convert an C# application to VB and have one issue which
>is
>converting the generic value to the default.
>C# uses return default(T) as the return value how would I translate this
>in
>VB.Net
>>
>Thanks

From what I've read, default(T) just gets the default value of the type.
So, in Visual Basic, as David Anton explains before me, the value of
"Nothing" should accomplish this same goal (reference types have a reference
to null (or Nothing in VB.Net) by default. Value types, when you set them
to Nothing, will be set to their default types (although, I think you
shouldn't be able to set a value type to Nothing....but that's just my
opinion :D ).

HTH,
Mythran

[Patrice]

How do you know it returns Nothing ?

I tried :

Class Program
Class Test
Shared Function GetDefaultValue(Of t)() As t
Return Nothing
End Function
End Class
Shared Sub Main()
MsgBox(Test.GetDefaultValue(Of Guid).ToString)
End Sub
End Class

And it looks like it returns an empty GUID.

IMO your best bet would to exoplain us what is the effect you have that
makes you think the returned value is not correct. Have you tried to check
IsNothing(MyValue) ?

--
Patrice
"cougaristic" <co*********@discussions.microsoft.coma écrit dans le
message de groupe de discussion :
F1**********************************@microsoft.com...

Just to learn more about this situation I would like to know how to handle
the following to return the 'actual' default for the generic type used.

When I am using Guid as the generic value like the following:
GetMessageHeader(Of Guid)(message,name,ns) it currently returns nothing if
the else statement is reached? Wouldn't the default of a guid be a guid
type
containing all zeros?

Here is the converted code in question:

Public Shared Function GetMessageHeader(Of T)(ByVal message As Message,
ByVal name As String, ByVal ns As String) As T
Dim index As Integer = message.Headers.FindHeader(name, ns)
If (index -1) Then
Dim val As T = message.Headers.GetHeader(Of T)(name, ns)
Return val
Else
'The following is what this question is all about
'C# = default(T)
Return Nothing
End If
End Function

Thanks

"Mythran" wrote:

>>

"David Anton" <Da********@discussions.microsoft.comwrote in message
news:BD**********************************@microso ft.com...

'Nothing'.
This keyword is more general than the C# 'null', handling reference
types,
value types, and generic types.
--
http://www.tangiblesoftwaresolutions.com
C++ to C#
C++ to VB
C++ to Java
VB & C# to Java
Java to VB & C#
Instant C#: VB to C#
Instant VB: C# to VB
Instant C++: VB, C#, or Java to C++/CLI
"cougaristic" wrote:

I am trying to convert an C# application to VB and have one issue
which
is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate
this
in
VB.Net

Thanks

From what I've read, default(T) just gets the default value of the type.
So, in Visual Basic, as David Anton explains before me, the value of
"Nothing" should accomplish this same goal (reference types have a
reference
to null (or Nothing in VB.Net) by default. Value types, when you set
them
to Nothing, will be set to their default types (although, I think you
shouldn't be able to set a value type to Nothing....but that's just my
opinion :D ).

HTH,
Mythran

[=?Utf-8?B?Y291Z2FyaXN0aWM=?=]

For the sake of argument why should I always believe that the default for
anything is always null/or nothing?
If I was using a specialized business object for the generic object and it
had a default string field named MyDefault with a default of 'This is the
default value' then why should the method return null/nothing instead of
returning the value 'This is the default value'?

This is just a question to help me understand what the real difference is
between the default(t) vs returning Null/Nothing. If default(t) always
returns null/nothing as shown in my example code then why not just return
null/nothing all of the time?

"Patrice" wrote:

How do you know it returns Nothing ?

I tried :

Class Program
Class Test
Shared Function GetDefaultValue(Of t)() As t
Return Nothing
End Function
End Class
Shared Sub Main()
MsgBox(Test.GetDefaultValue(Of Guid).ToString)
End Sub
End Class

And it looks like it returns an empty GUID.

IMO your best bet would to exoplain us what is the effect you have that
makes you think the returned value is not correct. Have you tried to check
IsNothing(MyValue) ?

--
Patrice
"cougaristic" <co*********@discussions.microsoft.coma crit dans le
message de groupe de discussion :
F1**********************************@microsoft.com...

Just to learn more about this situation I would like to know how to handle
the following to return the 'actual' default for the generic type used.

When I am using Guid as the generic value like the following:
GetMessageHeader(Of Guid)(message,name,ns) it currently returns nothing if
the else statement is reached? Wouldn't the default of a guid be a guid
type
containing all zeros?

Here is the converted code in question:

Public Shared Function GetMessageHeader(Of T)(ByVal message As Message,
ByVal name As String, ByVal ns As String) As T
Dim index As Integer = message.Headers.FindHeader(name, ns)
If (index -1) Then
Dim val As T = message.Headers.GetHeader(Of T)(name, ns)
Return val
Else
'The following is what this question is all about
'C# = default(T)
Return Nothing
End If
End Function

Thanks

"Mythran" wrote:

>

"David Anton" <Da********@discussions.microsoft.comwrote in message
news:BD**********************************@microsof t.com...
'Nothing'.
This keyword is more general than the C# 'null', handling reference
types,
value types, and generic types.
--
http://www.tangiblesoftwaresolutions.com
C++ to C#
C++ to VB
C++ to Java
VB & C# to Java
Java to VB & C#
Instant C#: VB to C#
Instant VB: C# to VB
Instant C++: VB, C#, or Java to C++/CLI
"cougaristic" wrote:

I am trying to convert an C# application to VB and have one issue
which
is
converting the generic value to the default.
C# uses return default(T) as the return value how would I translate
this
in
VB.Net

Thanks

From what I've read, default(T) just gets the default value of the type.
So, in Visual Basic, as David Anton explains before me, the value of
"Nothing" should accomplish this same goal (reference types have a
reference
to null (or Nothing in VB.Net) by default. Value types, when you set
them
to Nothing, will be set to their default types (although, I think you
shouldn't be able to set a value type to Nothing....but that's just my
opinion :D ).

HTH,
Mythran

[Patrice]

For the sake of argument why should I always believe that the default for

anything is always null/or nothing?

This is just a notation ie. :

Dim i As Integer=Nothing

will just affect the default value for the integer datatype which is 0. Note
that the actual value for the i variable is *NOT* "Nothing" but 0 which is
the default value for integers. Actually my personal preference would be to
avoid this confusing notation (you could have Dim DefaultValue As T and
later Return DefaultValue in your code, it will return the default value
without using the confusing Nothing notation). In particular it certainly
doesn't apply to C#. This is just how VB handles Nothing affectation...

If I was using a specialized business object for the generic object and it
had a default string field named MyDefault with a default of 'This is the
default value' then why should the method return null/nothing instead of
returning the value 'This is the default value'?

Which method ? Generally this kind of default value is defined using an
attribute and could be retrieved by reading this attribute (for example this
is done for default values when creating controls whose values are set using
the property grid dialog). Here we are talking about the language default
value for a particular type that knows only about the type default value...

This is just a question to help me understand what the real difference is
between the default(t) vs returning Null/Nothing. If default(t) always
returns null/nothing as shown in my example code then why not just return
null/nothing all of the time?

Not sure what you meant. My code was confusing ? It was to show that for the
GUID type returning Nothing will actually produce an empty GUID which is the
default value for this type. So the code (and your code) works as you wish ?

So IMO you should restart fresh . For now my understanding is that you just
don't like to translate "default (T)" by "Return Nothing" because you think
that the GUID value would be then "Nothing" rather than an empty GUID. This
is just not the case.

You won't have this problem. Affecting Nothing to a variable just set the
variable to its default value (which is not necessarily the "real" Nothing
value).

If you run your code, does it produce the result you want ? (my
understanding is that the problem is the confusing Nothing affectation that
doesn't really affect "Nothing" the value but whatever default value for the
assigned variable).
--
Patrice