Need advice please.With-End With

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Tim - 21 Mar 2007 15:20 GMT

Is there any performance advantage if I follow example 2.
Which one is preferred.

Example 1
Dataset.Table.Column1.DefaultValue =SomeThing
Dataset.Table.Column2.DefaultValue =SomeThing
Dataset.Table.Column3.DefaultValue =SomeThing
...
...

Example 2
With Dataset.Table
.Column1.DefaultValue=SomeThing
.Column2.DefaultValue=SomeThing
.Column3.DefaultValue=SomeThing
...
...
End With

Thanks for you suggestion you can provide.
Tim

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VJ - 21 Mar 2007 16:46 GMT

by MSDN doc..

"In Visual Basic you must usually specify an object in every statement that
calls one of its methods or accesses one of its properties. However, if you
have a series of statements that all operate on the same object, you can use
a With...End With structure to specify the object once for all of the
statements. This can make your procedures run faster and help you avoid
repetitive typing."

VJ

> Is there any performance advantage if I follow example 2.
> Which one is preferred.
[quoted text clipped - 17 lines]
> Thanks for you suggestion you can provide.
> Tim

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Jon Skeet [C# MVP] - 21 Mar 2007 21:11 GMT

> by MSDN doc..
>
[quoted text clipped - 4 lines]
> statements. This can make your procedures run faster and help you avoid
> repetitive typing."

Yes, but that doesn't explain *why* it's faster, which is because
writing out the same expression multiple times requires that the
expression (in this case DataSet.Table) is evaluated multiple times.
That can be avoided without using a "With" block just by using a local
variable.

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Jon Skeet [C# MVP] - 21 Mar 2007 21:10 GMT

> Is there any performance advantage if I follow example 2.
> Which one is preferred.
[quoted text clipped - 16 lines]
>
> Thanks for you suggestion you can provide.

There's a *tiny* performance improvement in the second, in that it's
not looking at the "Table" property each time. That's all. You could
easily get the same effect with:

DataTable table = Dataset.Table
table.Column1.DefaultValue=SomeThing
table.Column2.DefaultValue=SomeThing
table.Column3.DefaultValue=SomeThing

Personally that's what I'd do - I'm not a fan of "With".

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VJ - 21 Mar 2007 22:31 GMT

Ok I do certainly understand what you are saying.. so adding a variable is
in that one point additional memory space?.. and second point again doing
Table.Columns three times, that gets to have "table" ( your local variable)
evaluated 3 times.. so isn't With the better way than a local variable

Unless I missed the bigger picture here !

VJ

>> Is there any performance advantage if I follow example 2.
>> Which one is preferred.
[quoted text clipped - 27 lines]
>
> Personally that's what I'd do - I'm not a fan of "With".

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Jon Skeet [C# MVP] - 21 Mar 2007 23:06 GMT

> Ok I do certainly understand what you are saying.. so adding a variable is
> in that one point additional memory space?..

No, as they compile to the same code.

> and second point again doing Table.Columns three times, that gets to
> have "table" ( your local variable) evaluated 3 times..

Evaluating a local variable is very quick. Evaluating a property may
not be. That's the difference.

> so isn't With the better way than a local variable
>
> Unless I missed the bigger picture here !

Well, the bigger picture starts with the fact that With/End With gets
compiled to the same code as using a local variable. How else would you
expect the IL to look?

Compile the following code, and compare the compiled methods in ILDASM:

Public Class Foo

Dim x As String = "Hello"

Public Shared Sub Main
Dim y as new Foo
With y.x
Console.WriteLine (.Length)
Console.WriteLine (.Substring(1))
End With
End Sub

Public Shared Sub Main2
Dim y as new Foo
Dim s as String = y.x
Console.WriteLine (s.Length)
Console.WriteLine (s.Substring(1))
End Sub

End Class

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Jon Skeet - <skeet@pobox.com>
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VJ - 22 Mar 2007 02:41 GMT

Yes after I posted here that is what I did (write and check the ILDASM) and
got it. Thanks a lot for explaination Jon..

VJ

>> Ok I do certainly understand what you are saying.. so adding a variable
>> is
[quoted text clipped - 38 lines]
>
> End Class

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Tim - 22 Mar 2007 18:53 GMT

Thanks VJ and Jon.

> Yes after I posted here that is what I did (write and check the ILDASM)
> and got it. Thanks a lot for explaination Jon..
[quoted text clipped - 43 lines]
>>
>> End Class

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Need advice please.With-End With

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