Initializing Member Variables of Class ...

  • Thread starter Thread starter Joe HM
  • Start date Start date
J

Joe HM

Hello -

I was wondering what the proper way is to initialize member variables
of a Class. Here is the code ...

Public Class
Private mX As Single = Single.NaN
...

Public Sub New()
mX = Single.NaN
End Sub
End Class

Do I need the New in this case or is it fine to just initialize them
with the declaration? Which is the better style?

Thanks!
Joe
 
Hello -

I was wondering what the proper way is to initialize member variables
of a Class.  Here is the code ...

Public Class
  Private mX As Single = Single.NaN
  ...

  Public Sub New()
    mX = Single.NaN
  End Sub
End Class

Do I need the New in this case or is it fine to just initialize them
with the declaration?  Which is the better style?
Click to expand...

That question has been asked several times already, and the range of
answers generally boil down to "have it your way".

But if you expect to serialize or deserialize the class it is my
impression that you must have a constructor with no parameters.

Personally, I prefer to initialize class members in the constructor.
 
Hello -

I was wondering what the proper way is to initialize member variables
of a Class.  Here is the code ...

Public Class
  Private mX As Single = Single.NaN
  ...

  Public Sub New()
    mX = Single.NaN
  End Sub
End Class

Do I need the New in this case or is it fine to just initialize them
with the declaration?  Which is the better style?

Thanks!
Joe
Click to expand...

One thing to remember is that you must chain constructors when you
have multiple ways of instantiating the class. This is pretty simple
to do, you just have to remember to do it.

Just in case you or others readers don't know, the pattern is:

///////////
Public Sub New()
Me.Foo = "bar"
End Sub

Public Sub New(barValue as String)
Me.New()

Me.Bar = barValue
End Sub
///////////

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
That question has been asked several times already, and the range of
answers generally boil down to "have it your way".

But if you expect to serialize or deserialize the class it is my
impression that you must have a constructor with no parameters.

Personally, I prefer to initialize class members in the constructor.- Hide quoted text -

- Show quoted text -
Click to expand...

Hello -

Makes sense ... thanks for the feedback!

Joe
 
One thing to remember is that you must chain constructors when you
have multiple ways of instantiating the class. This is pretty simple
to do, you just have to remember to do it.

Just in case you or others readers don't know, the pattern is:

///////////
Public Sub New()
  Me.Foo = "bar"
End Sub

Public Sub New(barValue as String)
  Me.New()

  Me.Bar = barValue
End Sub
///////////

Thanks,

Seth Rowe [MVP]http://sethrowe.blogspot.com/- Hide quoted text -

- Show quoted text -
Click to expand...

Hello -

I didn't even think about that case ... Thanks!

Joe
 
(For some reason OE is no longer putting a > in col. 1 of the post I am
replying to. You'll find my reply appended below following the ===s.)

Hello -

I was wondering what the proper way is to initialize member variables
of a Class. Here is the code ...

Public Class
Private mX As Single = Single.NaN
...

Public Sub New()
mX = Single.NaN
End Sub
End Class

Do I need the New in this case or is it fine to just initialize them
with the declaration? Which is the better style?

Thanks!
Joe
Click to expand...

One thing to remember is that you must chain constructors when you
have multiple ways of instantiating the class. This is pretty simple
to do, you just have to remember to do it.

Just in case you or others readers don't know, the pattern is:

///////////
Public Sub New()
Me.Foo = "bar"
End Sub

Public Sub New(barValue as String)
Me.New()

Me.Bar = barValue
End Sub
///////////

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/

========== Reply from eBob.com ========================

Hi Seth,

Can you elaborate a bit. When you say "must" ... does that mean that I will
see a compiler error if I violate the rule? Also, when you say "chain" do
you mean what I'll call a strict chain in which if I have n+1 constructors,
0-n, the sequence will always be 0 or 1,0 or 2,1,0 or 3,2,1,0 or ... or
n,n-1,...,0?

Thanks, Bob
 
(For some reason OE is no longer putting a > in col. 1 of the post I am
replying to.  You'll find my reply appended below following the ===s.)
Click to expand...

Apparently Google is screwing around with their message formatting
again (I post exclusively through groups.google.com)!
Can you elaborate a bit.  When you say "must" ... does that mean that Iwill
see a compiler error if I violate the rule?
Click to expand...

Nope, you would just end up with some uninitialized variables.
 Also, when you say "chain" do
you mean what I'll call a strict chain in which if I have n+1 constructors,
0-n, the sequence will always be 0 or 1,0 or 2,1,0 or 3,2,1,0 or ... or
n,n-1,...,0?
Click to expand...

Nope, no calling order is enforced.

It's more of a DRY (don't repeat yourself) thing than anything. It
would be bad design (imo) to have the same variable initialization
routines in every constructor, so you basically have two options.
First is to have a sub routine that does the initialization, this sub
routine would need to be called by every constructor (better, but
still bad). The second option would be to have one root constructor,
usually parameterless and private if need be, that does the
initialization and then all other constructors (where it makes sense)
call into that one, either directly or through a chain.

For example, consider this class's constructors:

//////////////
Public Class Report

Private Sub New()
_CreatedDate = DateTime.Now()
End Sub

Public Sub New(creator As String)
'// Initializes CreateTime
Me.New()

_Creator = creator
End Sub

Public Sub New(creator As String, createdDate As DateTime)
'// Custom initialization, no constructors called
_Creator = creator
_CreatedDate = createdDate
End Sub

Public Sub New(reportToClone As Report)
'// Break down complex object into another constructor call
Me.New(reportToClone.Creator, reportToClone.CreatedDate)
End Sub

End Class
/////////////

That should demonstrate several ways constructor chaining would be
desirable, and a few where it wouldn't be.

I also forgot to weigh in on the original question. Personally, I
always initialize the local variable directly and rarely through the
constructor (unless of course the values are being passed in).

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
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