which approach outperforms the other ?

[tinman]

Hi...

I have the following two excerpts from a method. It basically reads data
from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _
DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String)
End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I
find
that at each DirectCast, there is unboxing but in Excerpt B, there isn't
any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32
[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F
romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with
regards to
casting would be much appreciated as well.

Cheers !

[CJ Taylor]

This is mearly a guess at best...but I would like to learn this as well...

I would assume the direct cast would be faster (mainly because I know direct
cast is faster) and also this call

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F
romObject(objec t)

I would figure that FromObject is a class and created on the heap. I would
also assume there is more code inside that method that takes longer to
execute. Whereas the unbox (I don't know what that means necessarily) seems
pretty direct. I don't know, just assuming.

I think it would be helpful to see the dissassembly from the FromObject
method to be 100% sure.

HTH,
CJ

"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...

Hi...

I have the following two excerpts from a method. It basically reads data
from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _
DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String)
End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I
find
that at each DirectCast, there is unboxing but in Excerpt B, there isn't
any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32
[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with
regards to
casting would be much appreciated as well.

Cheers !

[Jay B. Harlow [MVP - Outlook]]

Tinman,
In addition to the earlier answers William and I gave, the first is more
correct, although I would use the technique I gave in my first response here
instead of DirectCast.

Using Option Strict On, which requires the first, is more "correct", in that
you are stating that project_id is a GUID, start date is a DateTime... You
are not allowing the compiler make that decision for you...

Also using Option Strict On allows you to catch a number of errors at
compile time, instead of run time.

Hope this helps
Jay

"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...

Hi...

I have the following two excerpts from a method. It basically reads data
from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _
DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String)
End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I
find
that at each DirectCast, there is unboxing but in Excerpt B, there isn't
any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32
[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with
regards to
casting would be much appreciated as well.

Cheers !

[tinman]

thanks guys....

I believe the Get*Type* works better than the DirectCast approach. The
resulting
IL appears "leaner"...

In the initial IL with DirectCast, I was afraid that all the unboxing would
cause a performance
concern since it was going to continue reading data in a loop (While .Read)
........

Cheers...
"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...

Hi...

I have the following two excerpts from a method. It basically reads data
from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _
DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String)
End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I
find
that at each DirectCast, there is unboxing but in Excerpt B, there isn't
any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32
[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with
regards to
casting would be much appreciated as well.

Cheers !

[CJ Taylor]

Alright, maybe this is a dumb question, but what is unboxing?
"tinman" <dw****@yahoo.c om> wrote in message
news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..

thanks guys....

I believe the Get*Type* works better than the DirectCast approach. The
resulting
IL appears "leaner"...

In the initial IL with DirectCast, I was afraid that all the unboxing would cause a performance
concern since it was going to continue reading data in a loop (While ..Read) .......

Cheers...
"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...

Hi...

I have the following two excerpts from a method. It basically reads data
from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _
DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String)
End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I find
that at each DirectCast, there is unboxing but in Excerpt B, there isn't
any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F

romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with
regards to
casting would be much appreciated as well.

Cheers !

[Jay B. Harlow [MVP - Outlook]]

CJ,
When you assign a value type to an Object variable that type is boxed. Which
copies the value of the value type to an object on the heap.

When you then assign this Object variable back to the value type variable,
the object is unboxed.

Dim i As Integer
i = 100
Dim o As Object
o = i ' this causes the 100 to be boxed.

i = o ' this causes the boxed 100 to be unboxed

Of course if you have Option Strict On, you need DirectCast

i = DirectCast(o, Integer)

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:Op******** ********@TK2MSF TNGP09.phx.gbl. ..

Alright, maybe this is a dumb question, but what is unboxing?
"tinman" <dw****@yahoo.c om> wrote in message
news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..

thanks guys....

I believe the Get*Type* works better than the DirectCast approach. The
resulting
IL appears "leaner"...

In the initial IL with DirectCast, I was afraid that all the unboxing would

cause a performance
concern since it was going to continue reading data in a loop (While

.Read)

.......

Cheers...
"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...

Hi...

I have the following two excerpts from a method. It basically reads data from a DataReader and
loads it in a collection.
Excerpt A:
********
With ProjectData
While .Read
Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
DirectCast(.Ite m("start_date") , DateTime), _ DirectCast(.Ite m("end_date") , DateTime), _
DirectCast(.Ite m("priority") , Integer), _
DirectCast(.Ite m("description" ), String), _
DirectCast(.Ite m("project_mana ger"), String) End While
End With


Excerpt B:
********
With ProjectData
While .Read
Me.Add(.Item("p roject_id"),
.Item("start_da te"),
.Item("end_date "),
.Item("priority "),
.Item("descript ion"),
.Item("project_ manager")
End While
End With

Question:

Does automatic casting outperform explicit casting ? When I run ILDASM, I

find
that at each DirectCast, there is unboxing but in Excerpt B, there

isn't any.

Snippets of the ILDASM for Excerpt A and B below:

ILDASM (Excerpt A)
*************** *
IL_0098: ldloc.2
IL_0099: ldstr "descriptio n"
IL_009e: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_00a3: unbox [mscorlib]System.Int32
IL_00a8: ldobj [mscorlib]System.Int32
ILDASM (Excerpt B)
*************** *
IL_0092: ldloc.2
IL_0093: ldstr "descriptio n"
IL_0098: callvirt instance object
XXX.Projects.XD ataReader::get_ Item(string)
IL_009d: call int32

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F

romObject(objec t)

Any pointers to articles that explain what goes on "under the hood" with regards to
casting would be much appreciated as well.

Cheers !

[CJ Taylor]

Helps tremendously. Thanks for the info on that one Jay.

I think the best way to see it "visually" would be when your watching a
variable (in the watch window) of a base type (i.e. DataRow) thats actually
inherited (i.e MyDataRow of a dataset)

Where it shows your +- graphic and says its a datarow, then there is a sub
type underneath it that tells the actual class type that it is.

I hope that made sense. But again I appreciate your explanation.

So is unboxing an expensive process? given its only a single line of IL but
was curious if it was or not.


"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message
news:OL******** ******@TK2MSFTN GP10.phx.gbl...

CJ,
When you assign a value type to an Object variable that type is boxed. Which copies the value of the value type to an object on the heap.

When you then assign this Object variable back to the value type variable,
the object is unboxed.

Dim i As Integer
i = 100
Dim o As Object
o = i ' this causes the 100 to be boxed.

i = o ' this causes the boxed 100 to be unboxed

Of course if you have Option Strict On, you need DirectCast

i = DirectCast(o, Integer)

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:Op******** ********@TK2MSF TNGP09.phx.gbl. ..

Alright, maybe this is a dumb question, but what is unboxing?
"tinman" <dw****@yahoo.c om> wrote in message
news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..

thanks guys....

I believe the Get*Type* works better than the DirectCast approach. The
resulting
IL appears "leaner"...

In the initial IL with DirectCast, I was afraid that all the unboxing would

cause a performance
concern since it was going to continue reading data in a loop (While

.Read)

.......

Cheers...
"tinman" <dw****@yahoo.c om> wrote in message
news:uh******** ******@TK2MSFTN GP12.phx.gbl...
> Hi...
>
> I have the following two excerpts from a method. It basically reads data > from a DataReader and
> loads it in a collection.
>
>
> Excerpt A:
> ********
> With ProjectData
> While .Read
> Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
> DirectCast(.Ite m("start_date") , DateTime), _

> DirectCast(.Ite m("end_date") , DateTime),

_ > DirectCast(.Ite m("priority") , Integer), _
> DirectCast(.Ite m("description" ), String), _ > DirectCast(.Ite m("project_mana ger"),

String) > End While
> End With
>
>
>
>
> Excerpt B:
> ********
> With ProjectData
> While .Read
> Me.Add(.Item("p roject_id"),
> .Item("start_da te"),
> .Item("end_date "),
> .Item("priority "),
> .Item("descript ion"),
> .Item("project_ manager")
> End While
> End With
>
>
>
> Question:
>
> Does automatic casting outperform explicit casting ? When I run ILDASM,

I

> find
> that at each DirectCast, there is unboxing but in Excerpt B, there

isn't > any.
>
> Snippets of the ILDASM for Excerpt A and B below:
>
> ILDASM (Excerpt A)
> *************** *
> IL_0098: ldloc.2
> IL_0099: ldstr "descriptio n"
> IL_009e: callvirt instance object
> XXX.Projects.XD ataReader::get_ Item(string)
> IL_00a3: unbox [mscorlib]System.Int32
> IL_00a8: ldobj [mscorlib]System.Int32
>
>
> ILDASM (Excerpt B)
> *************** *
> IL_0092: ldloc.2
> IL_0093: ldstr "descriptio n"
> IL_0098: callvirt instance object
> XXX.Projects.XD ataReader::get_ Item(string)
> IL_009d: call int32
>

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F

> romObject(objec t)
>
> Any pointers to articles that explain what goes on "under the hood" with > regards to
> casting would be much appreciated as well.
>
> Cheers !
>
>

[Jay B. Harlow [MVP - Outlook]]

CJ,

So is unboxing an expensive process? given its only a single line of IL but was curious if it was or not. Its expensive in that the value needs to be copied from the heap to the
variable.

Its also expensive in that the boxing itself created an object on the heap,
this object will later need to be Garbage collected.

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:%2******** *******@TK2MSFT NGP10.phx.gbl.. . Helps tremendously. Thanks for the info on that one Jay.

I think the best way to see it "visually" would be when your watching a
variable (in the watch window) of a base type (i.e. DataRow) thats actually inherited (i.e MyDataRow of a dataset)

Where it shows your +- graphic and says its a datarow, then there is a sub
type underneath it that tells the actual class type that it is.

I hope that made sense. But again I appreciate your explanation.

So is unboxing an expensive process? given its only a single line of IL but was curious if it was or not.


"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message
news:OL******** ******@TK2MSFTN GP10.phx.gbl...

CJ,
When you assign a value type to an Object variable that type is boxed. Which

copies the value of the value type to an object on the heap.

When you then assign this Object variable back to the value type variable,

the object is unboxed.

Dim i As Integer
i = 100
Dim o As Object
o = i ' this causes the 100 to be boxed.

i = o ' this causes the boxed 100 to be unboxed

Of course if you have Option Strict On, you need DirectCast

i = DirectCast(o, Integer)

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:Op******** ********@TK2MSF TNGP09.phx.gbl. ..

Alright, maybe this is a dumb question, but what is unboxing?
"tinman" <dw****@yahoo.c om> wrote in message
news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..
> thanks guys....
>
> I believe the Get*Type* works better than the DirectCast approach. The > resulting
> IL appears "leaner"...
>
> In the initial IL with DirectCast, I was afraid that all the unboxing would
> cause a performance
> concern since it was going to continue reading data in a loop (While
.Read)
> .......
>
> Cheers...
>
>
> "tinman" <dw****@yahoo.c om> wrote in message
> news:uh******** ******@TK2MSFTN GP12.phx.gbl...
> > Hi...
> >
> > I have the following two excerpts from a method. It basically reads

data

> > from a DataReader and
> > loads it in a collection.
> >
> >
> > Excerpt A:
> > ********
> > With ProjectData
> > While .Read
> > Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
> > DirectCast(.Ite m("start_date") , DateTime),

_

> > DirectCast(.Ite m("end_date") ,

DateTime), _ > > DirectCast(.Ite m("priority") , Integer),

_ > > DirectCast(.Ite m("description" ), String),

_ > > DirectCast(.Ite m("project_mana ger"),

String)

> > End While
> > End With
> >
> >
> >
> >
> > Excerpt B:
> > ********
> > With ProjectData
> > While .Read
> > Me.Add(.Item("p roject_id"),
> > .Item("start_da te"),
> > .Item("end_date "),
> > .Item("priority "),
> > .Item("descript ion"),
> > .Item("project_ manager")
> > End While
> > End With
> >
> >
> >
> > Question:
> >
> > Does automatic casting outperform explicit casting ? When I run

ILDASM,

I
> > find
> > that at each DirectCast, there is unboxing but in Excerpt B, there

isn't

> > any.
> >
> > Snippets of the ILDASM for Excerpt A and B below:
> >
> > ILDASM (Excerpt A)
> > *************** *
> > IL_0098: ldloc.2
> > IL_0099: ldstr "descriptio n"
> > IL_009e: callvirt instance object
> > XXX.Projects.XD ataReader::get_ Item(string)
> > IL_00a3: unbox [mscorlib]System.Int32
> > IL_00a8: ldobj [mscorlib]System.Int32
> >
> >
> > ILDASM (Excerpt B)
> > *************** *
> > IL_0092: ldloc.2
> > IL_0093: ldstr "descriptio n"
> > IL_0098: callvirt instance object
> > XXX.Projects.XD ataReader::get_ Item(string)
> > IL_009d: call int32
> >
>

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F > > romObject(objec t)
> >
> > Any pointers to articles that explain what goes on "under the

hood" with

> > regards to
> > casting would be much appreciated as well.
> >
> > Cheers !
> >
> >
>
>

[CJ Taylor]

Ok, last question I swear.

Alright, so unboxing takes a variable (more than likely on the heap in most
cases) and creates a copy of that on the heap again on the unboxing process.
And then has to be gc'd as well as the original value (if that original
value exists on the heap as well).

Hmmm...

Option Strict. =)

Thanks Jay!

-CJ

"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message
news:%2******** ********@TK2MSF TNGP12.phx.gbl. ..

CJ,

So is unboxing an expensive process? given its only a single line of IL but

was curious if it was or not.

Its expensive in that the value needs to be copied from the heap to the
variable.

Its also expensive in that the boxing itself created an object on the

heap, this object will later need to be Garbage collected.

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:%2******** *******@TK2MSFT NGP10.phx.gbl.. .

Helps tremendously. Thanks for the info on that one Jay.

I think the best way to see it "visually" would be when your watching a
variable (in the watch window) of a base type (i.e. DataRow) thats actually

inherited (i.e MyDataRow of a dataset)

Where it shows your +- graphic and says its a datarow, then there is a sub

type underneath it that tells the actual class type that it is.

I hope that made sense. But again I appreciate your explanation.

So is unboxing an expensive process? given its only a single line of IL

but

was curious if it was or not.


"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message news:OL******** ******@TK2MSFTN GP10.phx.gbl...

CJ,
When you assign a value type to an Object variable that type is boxed.

Which

copies the value of the value type to an object on the heap.

When you then assign this Object variable back to the value type

variable, the object is unboxed.

Dim i As Integer
i = 100
Dim o As Object
o = i ' this causes the 100 to be boxed.

i = o ' this causes the boxed 100 to be unboxed

Of course if you have Option Strict On, you need DirectCast

i = DirectCast(o, Integer)

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:Op******** ********@TK2MSF TNGP09.phx.gbl. ..
> Alright, maybe this is a dumb question, but what is unboxing?
>
>
> "tinman" <dw****@yahoo.c om> wrote in message
> news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..
> > thanks guys....
> >
> > I believe the Get*Type* works better than the DirectCast approach. The > > resulting
> > IL appears "leaner"...
> >
> > In the initial IL with DirectCast, I was afraid that all the unboxing > would
> > cause a performance
> > concern since it was going to continue reading data in a loop (While > .Read)
> > .......
> >
> > Cheers...
> >
> >
> > "tinman" <dw****@yahoo.c om> wrote in message
> > news:uh******** ******@TK2MSFTN GP12.phx.gbl...
> > > Hi...
> > >
> > > I have the following two excerpts from a method. It basically reads data
> > > from a DataReader and
> > > loads it in a collection.
> > >
> > >
> > > Excerpt A:
> > > ********
> > > With ProjectData
> > > While .Read
> > > Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
> > > DirectCast(.Ite m("start_date") ,

DateTime),

_
> > > DirectCast(.Ite m("end_date") , DateTime),

_

> > > DirectCast(.Ite m("priority") , Integer), _ > > > DirectCast(.Ite m("description" ), String),

_

> > > DirectCast(.Ite m("project_mana ger"),
String)
> > > End While
> > > End With
> > >
> > >
> > >
> > >
> > > Excerpt B:
> > > ********
> > > With ProjectData
> > > While .Read
> > > Me.Add(.Item("p roject_id"),
> > > .Item("start_da te"),
> > > .Item("end_date "),
> > > .Item("priority "),
> > > .Item("descript ion"),
> > > .Item("project_ manager")
> > > End While
> > > End With
> > >
> > >
> > >
> > > Question:
> > >
> > > Does automatic casting outperform explicit casting ? When I run
ILDASM,
> I
> > > find
> > > that at each DirectCast, there is unboxing but in Excerpt B,

there isn't
> > > any.
> > >
> > > Snippets of the ILDASM for Excerpt A and B below:
> > >
> > > ILDASM (Excerpt A)
> > > *************** *
> > > IL_0098: ldloc.2
> > > IL_0099: ldstr "descriptio n"
> > > IL_009e: callvirt instance object
> > > XXX.Projects.XD ataReader::get_ Item(string)
> > > IL_00a3: unbox [mscorlib]System.Int32
> > > IL_00a8: ldobj [mscorlib]System.Int32
> > >
> > >
> > > ILDASM (Excerpt B)
> > > *************** *
> > > IL_0092: ldloc.2
> > > IL_0093: ldstr "descriptio n"
> > > IL_0098: callvirt instance object
> > > XXX.Projects.XD ataReader::get_ Item(string)
> > > IL_009d: call int32
> > >
> >
>

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F

> > > romObject(objec t)
> > >
> > > Any pointers to articles that explain what goes on "under the hood" with
> > > regards to
> > > casting would be much appreciated as well.
> > >
> > > Cheers !
> > >
> > >
> >
> >
>
>

[Jay B. Harlow [MVP - Outlook]]

CJ,

Alright, so unboxing takes a variable (more than likely on the heap in most cases) By definition a boxed value is on the heap.
cases) and creates a copy of that on the heap again on the unboxing process.
No, not quite. Unboxing creates a copy of that value on the stack.
And then has to be gc'd as well as the original value (if that original
value exists on the heap as well). Correct the object that was created when the original value was boxed will
need to GC'd...

If you following the above, remember that a regular reference type (a Class)
can contain value types also, these values can also be boxed & unboxed,
however explaining it is a little more confusing ;-)

Option Strict has no real effect on Boxing & Unboxing.

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:uv******** ********@TK2MSF TNGP11.phx.gbl. .. Ok, last question I swear.

Alright, so unboxing takes a variable (more than likely on the heap in most cases) and creates a copy of that on the heap again on the unboxing process. And then has to be gc'd as well as the original value (if that original
value exists on the heap as well).

Hmmm...

Option Strict. =)

Thanks Jay!

-CJ

"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message
news:%2******** ********@TK2MSF TNGP12.phx.gbl. ..

CJ,

So is unboxing an expensive process? given its only a single line of IL

but

was curious if it was or not.

Its expensive in that the value needs to be copied from the heap to the
variable.

Its also expensive in that the boxing itself created an object on the

heap,

this object will later need to be Garbage collected.

Hope this helps
Jay

"CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
news:%2******** *******@TK2MSFT NGP10.phx.gbl.. .

Helps tremendously. Thanks for the info on that one Jay.

I think the best way to see it "visually" would be when your watching

a variable (in the watch window) of a base type (i.e. DataRow) thats

actually

inherited (i.e MyDataRow of a dataset)

Where it shows your +- graphic and says its a datarow, then there is a sub type underneath it that tells the actual class type that it is.

I hope that made sense. But again I appreciate your explanation.

So is unboxing an expensive process? given its only a single line of IL but

was curious if it was or not.


"Jay B. Harlow [MVP - Outlook]" <Ja************ @msn.com> wrote in message news:OL******** ******@TK2MSFTN GP10.phx.gbl...
> CJ,
> When you assign a value type to an Object variable that type is

boxed. Which
> copies the value of the value type to an object on the heap.
>
> When you then assign this Object variable back to the value type

variable,

> the object is unboxed.
>
> Dim i As Integer
> i = 100
> Dim o As Object
> o = i ' this causes the 100 to be boxed.
>
> i = o ' this causes the boxed 100 to be unboxed
>
> Of course if you have Option Strict On, you need DirectCast
>
> i = DirectCast(o, Integer)
>
> Hope this helps
> Jay
>
> "CJ Taylor" <[cege] at [tavayn] dit commmmm> wrote in message
> news:Op******** ********@TK2MSF TNGP09.phx.gbl. ..
> > Alright, maybe this is a dumb question, but what is unboxing?
> >
> >
> > "tinman" <dw****@yahoo.c om> wrote in message
> > news:%2******** ********@TK2MSF TNGP09.phx.gbl. ..
> > > thanks guys....
> > >
> > > I believe the Get*Type* works better than the DirectCast approach.

The

> > > resulting
> > > IL appears "leaner"...
> > >
> > > In the initial IL with DirectCast, I was afraid that all the

unboxing

> > would
> > > cause a performance
> > > concern since it was going to continue reading data in a loop

(While > > .Read)
> > > .......
> > >
> > > Cheers...
> > >
> > >
> > > "tinman" <dw****@yahoo.c om> wrote in message
> > > news:uh******** ******@TK2MSFTN GP12.phx.gbl...
> > > > Hi...
> > > >
> > > > I have the following two excerpts from a method. It basically

reads

> data
> > > > from a DataReader and
> > > > loads it in a collection.
> > > >
> > > >
> > > > Excerpt A:
> > > > ********
> > > > With ProjectData
> > > > While .Read
> > > > Me.Add(DirectCa st(.Item("proje ct_id"), Guid), _
> > > > DirectCast(.Ite m("start_date") ,
DateTime),
> _
> > > > DirectCast(.Ite m("end_date") ,

DateTime),

_
> > > > DirectCast(.Ite m("priority") , Integer),

_

> > > > DirectCast(.Ite m("description" ),

String),

_
> > > >

DirectCast(.Ite m("project_mana ger"), > String)
> > > > End While
> > > > End With
> > > >
> > > >
> > > >
> > > >
> > > > Excerpt B:
> > > > ********
> > > > With ProjectData
> > > > While .Read
> > > > Me.Add(.Item("p roject_id"),
> > > > .Item("start_da te"),
> > > > .Item("end_date "),
> > > > .Item("priority "),
> > > > .Item("descript ion"),
> > > > .Item("project_ manager")
> > > > End While
> > > > End With
> > > >
> > > >
> > > >
> > > > Question:
> > > >
> > > > Does automatic casting outperform explicit casting ? When I run > ILDASM,
> > I
> > > > find
> > > > that at each DirectCast, there is unboxing but in Excerpt B,

there > isn't
> > > > any.
> > > >
> > > > Snippets of the ILDASM for Excerpt A and B below:
> > > >
> > > > ILDASM (Excerpt A)
> > > > *************** *
> > > > IL_0098: ldloc.2
> > > > IL_0099: ldstr "descriptio n"
> > > > IL_009e: callvirt instance object
> > > > XXX.Projects.XD ataReader::get_ Item(string)
> > > > IL_00a3: unbox [mscorlib]System.Int32
> > > > IL_00a8: ldobj [mscorlib]System.Int32
> > > >
> > > >
> > > > ILDASM (Excerpt B)
> > > > *************** *
> > > > IL_0092: ldloc.2
> > > > IL_0093: ldstr "descriptio n"
> > > > IL_0098: callvirt instance object
> > > > XXX.Projects.XD ataReader::get_ Item(string)
> > > > IL_009d: call int32
> > > >
> > >
> >
>

[Microsoft.Visua lBasic]Microsoft.Visua lBasic.Compiler Services.Intege rType::F

> > > > romObject(objec t)
> > > >
> > > > Any pointers to articles that explain what goes on "under the

hood"

> with
> > > > regards to
> > > > casting would be much appreciated as well.
> > > >
> > > > Cheers !
> > > >
> > > >
> > >
> > >
> >
> >
>
>