Should I Use "Dim ___ As New ___"?

[Tim Baur]

Hi All,

I'm a VB6er who's recently started using VB2005; I have a general question
about variable declaration. In VB, I've always tried to avoid using the
"As New" construct when declaring a variable preferring instead to
instantiate in the class' or form's initialize event or as needed. Using
"As New" created unnecessary overhead and resulted in a loss of control
over my object's life cycle.

Is this advisable practice in .Net?
TIA
~Tim

[Scott M.]

There is a bit more flexibility in declaring first and instantiating second
that *may* be usefull in certain scenarios. Other than this, it doesn't
matter.

"Tim Baur" <tr**********@A RDyahoo.com> wrote in message
news:Xn******** *************** ***********@207 .46.248.16...

Hi All,

I'm a VB6er who's recently started using VB2005; I have a general question
about variable declaration. In VB, I've always tried to avoid using the
"As New" construct when declaring a variable preferring instead to
instantiate in the class' or form's initialize event or as needed. Using
"As New" created unnecessary overhead and resulted in a loss of control
over my object's life cycle.

Is this advisable practice in .Net?
TIA
~Tim

[jvb]

Using New is required except when using shared members of the class.
The new keyword creates a reference to the object that you are using.

[Armin Zingler]

"Tim Baur" <tr**********@A RDyahoo.com> schrieb

Hi All,

I'm a VB6er who's recently started using VB2005; I have a general
question about variable declaration. In VB, I've always tried to
avoid using the "As New" construct when declaring a variable
preferring instead to instantiate in the class' or form's initialize
event or as needed. Using "As New" created unnecessary overhead and
resulted in a loss of control over my object's life cycle.

Is this advisable practice in .Net?

The behavior is different. In VB6, "As New" means that the
object is created as soon as the variable is accessed. In VB.Net this does
not exist anymore. Now it means that the object is created as soon as the
variable is created. So, if you write

dim bla as new form

in a procedure, it is exactly the same as writing

dim bla as form
bla = new form
If you declare it at class level, it is exactly the same as writing

dim bla as form
'...
sub New()
bla = new form
end sub
See also:
http://msdn.microsoft.com/library/en...ctCreation.asp
Though, it is sometimes not advisable, but this is personal taste. I always
assume that the order of declaration doesn't matter. This is not true
anymore if the declaration contains a New statement. Example:

dim con as new oledbconnection (...)
dim cmd as new oledbcommand(co n)

You see that the app will fail if you change the order because the 2nd
statement depends on the 1st one.

Armin

[Tim Baur]

"Armin Zingler" <az*******@free net.de> wrote in
news:#m******** ******@TK2MSFTN GP10.phx.gbl:

The behavior is different. In VB6, "As New" means that the
object is created as soon as the variable is accessed. In VB.Net this
does not exist anymore. Now it means that the object is created as
soon as the ...

Thank you all for the input. Thanks for the thourough analysis, Armin.
This is good news -- I had hoped VB.Net would handle it this way.

[Cor Ligthert [MVP]]

Tim,

Dim ds as new Dataset
For each whatever
ds = new Dataset
'The first instanced object will only be cleaned up unused by the GC

Therefore you can do better
Dim ds as Dataset
For each whatever
ds = new dataset

Although when I don't need the dataset outside the loop I prefer even

For each whatever
dim ds as new Dataset

I hope this gives some ideas

Cor
"Tim Baur" <tr**********@A RDyahoo.com> schreef in bericht
news:Xn******** *************** ***********@207 .46.248.16...

Hi All,

I'm a VB6er who's recently started using VB2005; I have a general question
about variable declaration. In VB, I've always tried to avoid using the
"As New" construct when declaring a variable preferring instead to
instantiate in the class' or form's initialize event or as needed. Using
"As New" created unnecessary overhead and resulted in a loss of control
over my object's life cycle.

Is this advisable practice in .Net?
TIA
~Tim

[Tim Baur]

"Cor Ligthert [MVP]" <no************ @planet.nl> wrote in
news:uK******** ******@TK2MSFTN GP10.phx.gbl:

For each whatever
dim ds as new Dataset

In this example, ds scopes the loop and drops the reference on completion?
Nice, very C-ish.

This brings up a new question, if I followed the example above, wouldn't a
thousand whatevers result in ds being created a thousand times? A thousand
sets of variables on the stack, memory reservations, methods registered,
constructors running, etc.

If I instantiate ds outside the loop and reuse the reference, haven't I
saved effort?

[Herfried K. Wagner [MVP]]

"Tim Baur" <tr**********@A RDyahoo.com> schrieb:

I'm a VB6er who's recently started using VB2005; I have a general question
about variable declaration. In VB, I've always tried to avoid using the
"As New" construct when declaring a variable preferring instead to
instantiate in the class' or form's initialize event or as needed. Using
"As New" created unnecessary overhead and resulted in a loss of control
over my object's life cycle.

There is no difference between 'As New X()' and 'As X = New X()' in VB.NET
any more. Personally I prefer 'As New' because it makes code more compact.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://classicvb.org/petition/>

[Jim Wooley]

> "Tim Baur" <tr**********@A RDyahoo.com> schrieb

Hi All,

I'm a VB6er who's recently started using VB2005; I have a general
question about variable declaration. In VB, I've always tried to
avoid using the "As New" construct when declaring a variable
preferring instead to instantiate in the class' or form's initialize
event or as needed. Using "As New" created unnecessary overhead and
resulted in a loss of control over my object's life cycle.

Is this advisable practice in .Net?

The behavior is different. In VB6, "As New" means that the
object is created as soon as the variable is accessed. In VB.Net this
does
not exist anymore. Now it means that the object is created as soon as
the
variable is created. So, if you write
dim bla as new form

Not only that, but in VB6 if you re-referenced a variable which was previously
set to nothing, you would re-instantiate it. This was the main reason to
avoid the Dim x as New foo in VB 6. You no longer need to worry about that.

Jim Wooley

[Cor Ligthert [MVP]]

Tim,

This brings up a new question, if I followed the example above, wouldn't a
thousand whatevers result in ds being created a thousand times? A
thousand
sets of variables on the stack, memory reservations, methods registered,
constructors running, etc.

If I instantiate ds outside the loop and reuse the reference, haven't I
saved effort?

That was why I showed it, in all those except the first will the same amount
of ds be instanced. In the first sample is that plus 1. However why bother
you are using managed code that is especially for this.

Cor