DateTime Declaration

[Bob Day]

using VS 2003, VB.net...

Why is this valid:
dim x as datetime = nothing

but this is invalid:

public sub DoSomething (Optional byval x as datetime = nothing)
....code to do something
end sub

Nothing shows are error message that you cannot set a system object to
nothing.

Is there a work around for the sub problem? I must set it equal to
something since it is optional.

Thanks!
Bob Day

[Fergus Cooney]

Hi Bob,

Just to expand on your statement of the problem (which I consider
to be a bug*).

There is a problem setting an optional DateTime parameter to its
default value as illustrated with the following:

Sub Foo (ByRef Optional dtParam As DateTime = Nothing) 'Error
Dim dtLocal As DateTime = Nothing 'This is fine.
End Sub

The pre-compiler reports an error by underlining the Nothin in the
parameter list. The error given is:
Conversion from 'System.Object' to 'Date' cannot occur in a
constant expression.

The Visual Basic Language Reference says a lot about Nothing: :-)
The Nothing keyword represents the default value of any data
type. Assigning Nothing to a variable sets it to the default value for
its declared type. If that type contains variable members, they are
all set to their default values.

===============================
The workaround is to use a set date. The earliest DateTime is
12:00:00 midnight, January 1, 0001 C.E. (Common Era). Given that
you've found a bug, you could use #1/4/2003#.

Regards,
Fergus

=========================
*You wait months for a bug and nothing and all of a sudden - two in
one day!!

[Herfried K. Wagner [MVP]]

Hello,

"Bob Day" <Bo****@TouchTalk.net> schrieb:

using VS 2003, VB.net...

Why is this valid:
dim x as datetime = nothing

but this is invalid:

public sub DoSomething (Optional byval x as datetime = nothing)
....code to do something
end sub

Nothing shows are error message that you cannot set a system object to
nothing.

DateTime is a value type, so assigning Nothing doesn't make sense. The
default value will be assigned.

\\\
Dim d As Date = Nothing
MsgBox(IsNothing(d)) ' Returns False.
MsgBox(d.ToLongDateString())
///

HTH,
Herfried K. Wagner
--
MVP · VB Classic, VB .NET
http://www.mvps.org/dotnet

[Fergus Cooney]

Hi Herfried,

The pre-compiler gives an error.
If I may refer you to my response to the same query ? ...

Regards,
Fergus

[Herfried K. Wagner [MVP]]

Hello,

"Fergus Cooney" <fi******@tesco.net> schrieb:

The pre-compiler gives an error.
If Nothing is assigned in the parameter.
If I may refer you to my response to the same query ? ...

I know.

Regards,
Herfried K. Wagner
--
MVP · VB Classic, VB .NET
http://www.mvps.org/dotnet

[Herfried K. Wagner [MVP]]

Hello,

"Fergus Cooney" <fi******@tesco.net> schrieb:

Just to expand on your statement of the problem (which I consider
to be a bug*).

There is a problem setting an optional DateTime parameter to its
default value as illustrated with the following:

Sub Foo (ByRef Optional dtParam As DateTime = Nothing) 'Error
Dim dtLocal As DateTime = Nothing 'This is fine.
End Sub

The pre-compiler reports an error by underlining the Nothin in the
parameter list. The error given is:
Conversion from 'System.Object' to 'Date' cannot occur in a
constant expression.

The Visual Basic Language Reference says a lot about Nothing: :-)
The Nothing keyword represents the default value of any data
type. Assigning Nothing to a variable sets it to the default value for
its declared type. If that type contains variable members, they are
all set to their default values.
Have a look at the code below:

\\\
Const d As DateTime = Nothing
///

This code will cause the same error as assigning Nothing as the default
value of an optional parameter. I think the reason is that the compiler
won't do the conversion for you when compiling the application.
*You wait months for a bug and nothing and all of a sudden - two in
one day!!

I am not sure if this is a bug.

HTH,
Herfried K. Wagner
--
MVP · VB Classic, VB .NET
http://www.mvps.org/dotnet

[Bob Day]

I have read all your replies, and just to make things less clear, consider

Dim x As DateTime = DateTime.MinValue
Dim z As String = x.ToString

These should produce the same value, they do not. Hold your cursor over X
and you get only the time (and Locals in Debug shows the same). Hold your
cursor over X and you get the full date and time (and Locals window in debug
shows the same).

Why?

Bob Day

"Bob Day" <Bo****@TouchTalk.net> wrote in message
news:OC**************@TK2MSFTNGP11.phx.gbl...

using VS 2003, VB.net...

Why is this valid:
dim x as datetime = nothing

but this is invalid:

public sub DoSomething (Optional byval x as datetime = nothing)
....code to do something
end sub

Nothing shows are error message that you cannot set a system object to
nothing.

Is there a work around for the sub problem? I must set it equal to
something since it is optional.

Thanks!
Bob Day

[Armin Zingler]

"Bob Day" <Bo****@TouchTalk.net> schrieb

I have read all your replies, and just to make things less clear,
consider

Dim x As DateTime = DateTime.MinValue
Dim z As String = x.ToString

These should produce the same value, they do not. Hold your cursor
over X and you get only the time (and Locals in Debug shows the
same). Hold your cursor over X and you get the full date and time
(and Locals window in debug shows the same).

Why?

Because the tooltip in the IDE performs a different date-to-string
conversion from that you do.
--
Armin

[Bob Day]

It should not. As a developer, I cannot question when and where the tooltip
is giving me corrent results and when it is not. That is a bug, period.

Bob Day

"Armin Zingler" <az*******@freenet.de> wrote in message
news:OR**************@TK2MSFTNGP10.phx.gbl...

"Bob Day" <Bo****@TouchTalk.net> schrieb

I have read all your replies, and just to make things less clear,
consider

Dim x As DateTime = DateTime.MinValue
Dim z As String = x.ToString

These should produce the same value, they do not. Hold your cursor
over X and you get only the time (and Locals in Debug shows the
same). Hold your cursor over X and you get the full date and time
(and Locals window in

debug

shows the same).

Why?

Because the tooltip in the IDE performs a different date-to-string
conversion from that you do.
--
Armin

[Armin Zingler]

"Bob Day" <Bo****@TouchTalk.net> schrieb

It should not. As a developer, I cannot question when and where the
tooltip is giving me corrent results and when it is not. That is a
bug, period.

Yes, Sir!

The tooltip does give the right result.
#12:00:00 AM# is the format that is used in the IDE for datetime literals.
You can write, for example:

dim d as datetime
d = #12:00:00 AM#

The format is fixed because the code should be compliable in different
countries without changing the code (e.g. in Germany, we don't have "AM").
As the tooltip is shown by the IDE it also uses this format.
Then, we also have the "human readable" format depending on the
language/culture of the system (or the current thread). This format is used
because applicatoins should be "user friendly". _You_ are determining the
format used for datetime->string conversions. If you don't use the format
string to get the result you need, you don't have to wonder why the formats
are different.
--
Armin

[Armin Zingler]

"Armin Zingler" <az*******@freenet.de> schrieb

Yes, Sir!
I forgot the -> ;-) <-
The format is fixed because the code should be compliable in

....should be compilable...

In other words: The tooltip is for programmers, the result of the other
conversion for end users. => different formats.
--
Armin

[Cor]

Armin,

Yes, Sir!

That sounds better in the German language, can you speak that?
:-)
Cor

[Armin Zingler]

"Cor" <no*@non.com> schrieb

Armin,

Yes, Sir!

That sounds better in the German language, can you speak that?
:-)
Cor

?? what do you mean?

;-)

--
Armin

[Herfried K. Wagner [MVP]]

Hello,

"Cor" <no*@non.com> schrieb:

Yes, Sir!

That sounds better in the German language, can you speak
that?

What do you expect to hear?

--
Herfried K. Wagner
MVP · VB Classic, VB.NET
http://www.mvps.org/dotnet

[Cor]

Armin,
When "Jawoll Mijnherr" oder etwas is written I see in mind somebody clicking
his shoes together standing straight,
In the English language I see "yes sir" just as an polite acknowledge.
But maybe that is only in my mind.
:-)))
Cor