"ref object a" <> "ByRef a As Object" ???

[Dr Duck]

GDay all,

Something seems odd to me....
I wrote a simple C# function

public void bind(ref object a, ref object b, bool atob)
{
if(atob)
b = a;
else
a = b;
}

I call it from a windows app.

string data = "moo";
bind(ref (object)this.Te xt, ref (object)data, false);

As I expected I got Error CS1510 "A ref or out argument must be an
lvalue".
Here is what I didnt't expect, when I wrote a vb.net equivilant:

Public Sub bind(ByRef a As Object, ByRef b As Object, ByVal atob As
Boolean)
If (atob) Then
b = a
Else
a = b
End If
End Sub

and call it from a windows app:

Dim data As String = "moo"
bind(Me.Text, data, False)

Not only did it compile it also executed and worked - the forms title
was changed to "moo".

Why does VB.NET not spit the dummy?
Is it possible to coax C# into doing whatever vb did?

-DM

[Jon Skeet [C# MVP]]

Dr Duck <sh********@opt usnet.com.au> wrote:

<snip>

Here is what I didnt't expect, when I wrote a vb.net equivilant:

Public Sub bind(ByRef a As Object, ByRef b As Object, ByVal atob As
Boolean)
If (atob) Then
b = a
Else
a = b
End If
End Sub

and call it from a windows app:

Dim data As String = "moo"
bind(Me.Text, data, False)

Not only did it compile it also executed and worked - the forms title
was changed to "moo".

Why does VB.NET not spit the dummy?
Is it possible to coax C# into doing whatever vb did?

I've had a look at what VB.NET does under the covers, and basically it
creates temporary objects, passes those by reference, and then sets
data and Me.Text to the results afterwards. Utterly horrible, if you
ask me... but it only does it that way if the parameters are either
properties or subtypes of the formal parameter types.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Dr Duck]

Thanks Mate

I agree this "late bound tempory object" [made up term] thing sounds Horrible

I can't see the rational behind it

It sounds like it would cause a lot of problems in a multi threaded app
- assignment after the function call exits not being semaphore aware..
- a process comunicating to another it had modified the object referenced as a parameter
but the modification is not apparent as the process has not exited yet...

-DM

[Cor Ligthert]

Hi Jon,

I was yesterday suprissed reading that you did in the thread C# learner give
an advice to look for VB.net, that I never did expect, however you sees how
things can change. (no comments needed, I most probably know them already)

:-)

However when this message would come in the newsgroup languages.VB it would
get a lot of comments.

1. passing "by ref" from an Object, did you not try once to get me in a
discussion about boxing?.
2. passing as an Object
3. not Option Strict On.

I understand that it is a theoretical question, however I did want to add
this, because I did not see it in your comment, while this program will run
probably 10 times as slow as it could be.

What is something you make me always attent on when I forget by instance to
Xor a bit and do an "if" instead.

(And this part is not the area I like)

:-)

Cor

Public Sub bind(ByRef a As Object, ByRef b As Object, ByVal atob As
Boolean)
If (atob) Then
b = a
Else
a = b
End If
End Sub

[Jon Skeet [C# MVP]]

Cor Ligthert <no**********@p lanet.nl> wrote:

However when this message would come in the newsgroup languages.VB it would
get a lot of comments.

1. passing "by ref" from an Object, did you not try once to get me in a
discussion about boxing?.
Um, can't remember... is it important? There's no boxing going on here,
as there are no value types.
2. passing as an Object
What about it?
3. not Option Strict On.
Ah - didn't check that one. (Silly default, to have it off.) Yup, that
improves things *slightly*. It doesn't stop you from passing a property
by reference, although it does stop you from passing a string parameter
by reference to a method accepting the parameter as an object by
reference. In other words, it gets rid of half of the nastiness, but
not all of it.
I understand that it is a theoretical question, however I did want to add
this, because I did not see it in your comment, while this program will run
probably 10 times as slow as it could be.
I'm not sure I'd go along with that bit. It's not like it's using
reflection anywhere, for instance - it's just fetching a property and
assigning it again afterwards, which may *sometimes* be expensive, but
certainly doesn't have to be.
What is something you make me always attent on when I forget by instance to
Xor a bit and do an "if" instead.

(And this part is not the area I like)

No idea what you meant by that, but never mind.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Cor Ligthert]

Hi Jon,

1. passing "by ref" from an Object, did you not try once to get me in a
discussion about boxing?.

This are not the subjects (area) I like I said, so when I am wrong, I can
this time (at start) only believe you, however in VB is an object normaly
passed by value.

Because that value is its reference. I thought that when you do a passing by
reference, you are boxing that value (which is the reference).

However I am not sure about it, because I never would think about to pass a
reference of a reference.

Cor

[Jon Skeet [C# MVP]]

Cor Ligthert <no**********@p lanet.nl> wrote:

1. passing "by ref" from an Object, did you not try once to get me in a
discussion about boxing?.

This are not the subjects (area) I like I said, so when I am wrong, I can
this time (at start) only believe you, however in VB is an object normaly
passed by value.

Because that value is its reference. I thought that when you do a passing by
reference, you are boxing that value (which is the reference).
No, you aren't. Boxing is an entirely different concept. Boxing takes a
value type, and creates a new object on the heap containing that value.
It has nothing to do with pass-by-reference semantics.
However I am not sure about it, because I never would think about to pass a
reference of a reference.

Why not? It makes perfect sense in some situations.

See http://www.pobox.com/~skeet/csharp/parameters.html for more general
discussion of what pass-by-reference and pass-by-value mean, admittedly
in C# terms.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Cor Ligthert]

Hi Jon,

Because about some things I readed from Jay B Harlow I am not sure of your
message.

However I cannot deny it now. So maybe, ( because it does not intrest me
that much) I will investigate it deeper and come back on this subject.

However it was intresting that you do not agree with it, makes investigating
maybe something I will do.

Why not? It makes perfect sense in some situations.

I have done in past a lot of references of pointers, however until now I see
in VB.net no pratical use of it.

Cor

[Jon Skeet [C# MVP]]

Cor Ligthert <no**********@p lanet.nl> wrote:

Because about some things I readed from Jay B Harlow I am not sure of your
message.
Which things, out of interest? Which thread?
However I cannot deny it now. So maybe, ( because it does not intrest me
that much) I will investigate it deeper and come back on this subject.

However it was intresting that you do not agree with it, makes investigating
maybe something I will do.

I'll look at it myself - if you could let me know what Jay's said.

Why not? It makes perfect sense in some situations.

I have done in past a lot of references of pointers, however until now I see
in VB.net no pratical use of it.

Here's an example I've used before:

public void SplitName (string wholeName, out string firstName,
out string lastName)

("out" and "ref" parameters are very similar, I hope you'll agree)

So for instance:

string first;
string last;

SplitName ("Jon Skeet", out first, out last)

would end up with first="Jon" and last="Skeet".

I'm sure you can think of similar situations.

Personally I don't use out/ref parameters very often anyway, but when I
do they're just as likely to be reference types as value types.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[cody]

> public void bind(ref object a, ref object b, bool atob)

{
if(atob)
b = a;
else
a = b;
}

I call it from a windows app.

string data = "moo";
bind(ref (object)this.Te xt, ref (object)data, false);

As I expected I got Error CS1510 "A ref or out argument must be an
lvalue".

The question is: Why isn't that allowed?

--
cody

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