Assigning a reference to a variable

Jon · Joined: 22 Aug 2007 Posts: 8

If I have a structure, for example:

struct Settings{
public string str;
public double doub1, doub2;
public int i1;
}

How do I assign the reference of i1 to a variable? I can easily do this by passing it as a ref int
to a function, but is there a way to do this without passing it to a function?

Archived from group: microsoft>public>dotnet>languages>csharp

Jon Skeet [C# MVP] · Joined: 08 Aug 2007 Posts: 27

On Nov 26, 4:44 pm, "Jon" wrote:
> If I have a structure, for example:
>
> struct Settings{
> public string str;
> public double doub1, doub2;
> public int i1;
>
> }
>
> How do I assign the reference of i1 to a variable? I can easily do this by passing it as a ref int
> to a function, but is there a way to do this without passing it to a function?

No. If you want a type to behave like a reference type, you should
make it a reference type to start with.

Jon

Tom Porterfield · Joined: 08 Aug 2007 Posts: 6

Jon wrote:
> If I have a structure, for example:
>
> struct Settings{
> public string str;
> public double doub1, doub2;
> public int i1;
> }
>
> How do I assign the reference of i1 to a variable? I can easily do this by passing it as a ref int
> to a function, but is there a way to do this without passing it to a function?

You can do it using unsafe code, but I wouldn't recommend that. If you
use unsafe code, the syntax is very similar to C++.

Settings sets = new Settings();
sets.i1 = 5;
int *x = &sets.i1;
*x = 6;

Console.WriteLine(sets.i1.ToString());
--
Tom Porterfield

Jon · Joined: 22 Aug 2007 Posts: 8

Thanks for your replies Jon + Tom.

I'm from a C background, but I don't really want to use unsafe code.

"If you want a type to behave like a reference type, you should make it a reference type to start
with." How do I make an integer a reference type?

Jon

"Jon" wrote in message @TK2MSFTNGP06.phx.gbl...
If I have a structure, for example:

struct Settings{
public string str;
public double doub1, doub2;
public int i1;
}

How do I assign the reference of i1 to a variable? I can easily do this by passing it as a ref int
to a function, but is there a way to do this without passing it to a function?

Marc Gravell · Joined: 08 Aug 2007 Posts: 20

> "If you want a type to behave like a reference type, you should make it a reference type to start
> with." How do I make an integer a reference type?

You don't; you make Settings a reference type by changing "struct" to
"class". It is normally *very* rare to write a "struct" in .net, and
usually relates to discreet (but possibly compound) "values" - such as
a CompexInt32 or TimeRange.

> How do I assign the reference of i1 to a variable?

There is no such thing as a reference of i1; you could "box" it, but
that changes the meaning.

> I can easily do this by passing it as a ref int

Actually, this does something different again... can I recommend you
read the following? (one of Jon's pages)

http://www.pobox.com/~skeet/csharp/parameters.html

Marc

Jon · Joined: 22 Aug 2007 Posts: 8

Thanks Marc. I read Jon Skeet's page a few weeks ago and found it very helpful.

I think my problem is that my mind thinks in C, and it's having some problems adapting to C#.

I'm a bit nervous about changing the structs (I have quite a few) to classes, since it might break
something.

Am I right in saying that I can get a reference to an array inside a struct? If so, would having a
single-element array work?

struct Settings{
public string str;
public double doub1, doub2;
public intRef[];
}

....

int[] int1 = new int[1];
intRef = int1;

"Marc Gravell" wrote in message @f3g2000hsg.googlegroups.com...
> "If you want a type to behave like a reference type, you should make it a reference type to start
> with." How do I make an integer a reference type?

You don't; you make Settings a reference type by changing "struct" to
"class". It is normally *very* rare to write a "struct" in .net, and
usually relates to discreet (but possibly compound) "values" - such as
a CompexInt32 or TimeRange.

> How do I assign the reference of i1 to a variable?

There is no such thing as a reference of i1; you could "box" it, but
that changes the meaning.

> I can easily do this by passing it as a ref int

Actually, this does something different again... can I recommend you
read the following? (one of Jon's pages)

http://www.pobox.com/~skeet/csharp/parameters.html

Marc

Peter Duniho · Joined: 08 Aug 2007 Posts: 84

On 2007-11-27 01:20:14 -0800, "Jon" said:

> [...]
> I'm a bit nervous about changing the structs (I have quite a few) to
> classes, since it might break something.

Like what?

IMHO, on the balance it's more likely that switching to classes will
_fix_ more things than it breaks. Smile

> Am I right in saying that I can get a reference to an array inside a
> struct? If so, would having a single-element array work?

Yes. But boy, what a hack.

It's hard to offer specific advice without specific information
regarding what you're trying to do here. But my general rule of thumb
is: if you find yourself hacking around a perceived limitation in the
language, your first thought should be that you simply haven't adapted
to the language yet and your time would be better-spent figuring out
what the language-friendly way to solve your design issue is.

It's not a perfect rule of thumb, but it's served me very well over the years.

You haven't explained in any detail why it is you want to be able to
pass an integer variable by reference, but it's likely that whatever
the reason, you're just going to make things hard on yourself later by
not learning and accepting the normal way of doing things in C# now.

Pete

Jeffrey Tan[MSFT] · Joined: 08 Aug 2007 Posts: 77

Hi Jon,

Do you mind to tell me why you want to assign an integer reference to
another variable? What is the type of the another variable? Yes, in .Net
any array is reference type, however, I do not think your
solution/workaround is neat and may cause some other problems.

If you tell us the reason for the requirement, there may be a better
solution for it. Thanks.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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Peter Webb · Joined: 05 Nov 2007 Posts: 1

"Marc Gravell" wrote in message @f3g2000hsg.googlegroups.com...
>> "If you want a type to behave like a reference type, you should make it a
>> reference type to start
>> with." How do I make an integer a reference type?
>
> You don't; you make Settings a reference type by changing "struct" to
> "class". It is normally *very* rare to write a "struct" in .net, and
> usually relates to discreet (but possibly compound) "values" - such as
> a CompexInt32 or TimeRange.
>

That's interesting. As a beginner, I haven't really used structs much at
all - just a couple for the purposes of seeing what they do. I haven't used
them more, because I couldn't actually see any benefit of structs over
classes (except possibly a microscopic performance gain). I have felt guilty
about this, as I am not using what appeared to be a major part of the
language.

Are you now telling me that I needn't feel guilty about pretty much ignoring
struct types?

Peter Duniho · Joined: 08 Aug 2007 Posts: 84

On 2007-11-27 18:53:25 -0800, "Peter Webb"
said:

> That's interesting. As a beginner, I haven't really used structs much
> at all - just a couple for the purposes of seeing what they do. I
> haven't used them more, because I couldn't actually see any benefit of
> structs over classes (except possibly a microscopic performance gain).
> I have felt guilty about this, as I am not using what appeared to be a
> major part of the language.
>
> Are you now telling me that I needn't feel guilty about pretty much
> ignoring struct types?

That's right. Smile

Actually, there are real benefits to using a struct in certain
situations. They can perform better in some cases. For example, when
you have a lot of them and can allocate an array to contain the
collection (e.g. an actual Array, or some generic collection that uses
an array to store the values).

Of course, being a value type, they can also reduce performance if used
inappropriately. And they have subtly different semantics than
reference types, which can result in hard-to-identify bugs (especially
if the structs are mutable).

I would say that in the long run, you'll probably want to at least
spend some time learning about structs, how they are different from
classes, and why you might use them. Even if you never use a struct,
you'll at least understand better why you're not using them. Also,
since a lot of what makes a struct different from a class is the same
as what makes any value type different from a class, understanding
structs will help you understand the other value types as well.

Pete

Jon · Joined: 22 Aug 2007 Posts: 8

Hi Jeffrey,

Thanks for offering to help.

I have a variable that I would like to use as a reference to different variables within my struct.

My original example struct was too generalised to show this, and although the following is a
simplification of my real code, it is closer to a concise but complete example...

struct Settings{
public int left, right, centre;
}

Settings set = new Settings();
int ref intRef ; // ILLEGAL C# STATEMENT - note the use of "ref"
if(???) intRef = set.left;
else if(???) intRef = set.right;
else intRef = set.centre;

Then I would change the value that intRef points to.

From my C perspective, If I can do this with an array, it seems reasonable to me that I should be
allowed to do it with an int. I cannot do anything dangerous (eg increment a pointer which might
then point to something invalid).

To repliers who have suggested using a class rather than a struct, I'm not sure if this would
actually with my example, but maybe you can advise on this.

Jon

""Jeffrey Tan[MSFT]"" wrote in message @TK2MSFTNGHUB02.phx.gbl...
Hi Jon,

Do you mind to tell me why you want to assign an integer reference to
another variable? What is the type of the another variable? Yes, in .Net
any array is reference type, however, I do not think your
solution/workaround is neat and may cause some other problems.

If you tell us the reason for the requirement, there may be a better
solution for it. Thanks.

Best regards,
Jeffrey Tan
Microsoft Online Community Support

Jon Skeet [C# MVP] · Joined: 08 Aug 2007 Posts: 27

On Nov 28, 2:53 am, "Peter Webb"
wrote:
> That's interesting. As a beginner, I haven't really used structs much at
> all - just a couple for the purposes of seeing what they do. I haven't used
> them more, because I couldn't actually see any benefit of structs over
> classes (except possibly a microscopic performance gain).

It's not really about performance gain, usually - it's about reference
type semantics vs value type semantics.

> I have felt guilty
> about this, as I am not using what appeared to be a major part of the
> language.
>
> Are you now telling me that I needn't feel guilty about pretty much ignoring
> struct types?

Well, you're not *really* ignoring structs - you're just not creating
your *own* struct types.
Whenever you use int, Guid, long, float, byte etc you're using
structs.

It's a bit like generics - many people will never need to write their
own generic type or generic method (although I'd argue there's often a
lot of benefit for doing so) - but they may well *use* the existing
generic collections.

Jon

Jon · Joined: 22 Aug 2007 Posts: 8

Hi Peter

"Like what?" I don't actually know - I'm following the "if it ain't broke, don't fix it" philosophy
at the moment. I'm curious about your comment that switching to classes will fix more things than it
breaks. Are structs really that delicate?

"Yes. But boy, what a hack." I agree.

"you simply haven't adapted to the language yet and your time would be better-spent figuring out
what the language-friendly way to solve your design issue is" I agree - see the extra details I've
given in my reply to Jeffrey's question.

Thanks for you help,

Jon

"Peter Duniho" wrote in message @NnOwSlPiAnMkcom...
On 2007-11-27 01:20:14 -0800, "Jon" said:

> [...]
> I'm a bit nervous about changing the structs (I have quite a few) to
> classes, since it might break something.

Like what?

IMHO, on the balance it's more likely that switching to classes will
_fix_ more things than it breaks. Smile

> Am I right in saying that I can get a reference to an array inside a
> struct? If so, would having a single-element array work?

Yes. But boy, what a hack.

It's hard to offer specific advice without specific information
regarding what you're trying to do here. But my general rule of thumb
is: if you find yourself hacking around a perceived limitation in the
language, your first thought should be that you simply haven't adapted
to the language yet and your time would be better-spent figuring out
what the language-friendly way to solve your design issue is.

It's not a perfect rule of thumb, but it's served me very well over the years.

You haven't explained in any detail why it is you want to be able to
pass an integer variable by reference, but it's likely that whatever
the reason, you're just going to make things hard on yourself later by
not learning and accepting the normal way of doing things in C# now.

Pete

Peter Duniho · Joined: 08 Aug 2007 Posts: 84

On 2007-11-28 03:16:33 -0800, "Jon" said:

> Hi Peter
>
> "Like what?" I don't actually know - I'm following the "if it ain't
> broke, don't fix it" philosophy at the moment. I'm curious about your
> comment that switching to classes will fix more things than it breaks.
> Are structs really that delicate?

It's not so much that they are delicate, but that they are in some ways
significantly different from classes, even as they look very similar.
For a person just learning C#, it's possible that just as you find
yourself getting comfortable with the "reference-only" nature of
classes (something that's necessary for effective C# programming),
something specific about the value-type nature of structs will be
overlooked, resulting in a confusing bug.

This can especially problematic for someone experienced in C++
programming, where there's no real difference between a struct and a
class except for default accessibility. In C#, structs and classes
fill very specific roles, different from each other.

I didn't mean to give the impression that structs are somehow a fragile
way to code. They aren't. It's just that they a different enough from
classes that it's not hard to get confused about how to use them,
especially for someone new to the language (and I'm not just saying
this in an abstract way...I was once new to the language myself, and I
still remember the process of figuring out the implications of the
difference between a value type and a reference type).

Pete

Peter Duniho · Joined: 08 Aug 2007 Posts: 84

On 2007-11-28 03:04:23 -0800, "Jon" said:

> Hi Jeffrey,
>
> Thanks for offering to help.
>
> I have a variable that I would like to use as a reference to different
> variables within my struct.
>
> My original example struct was too generalised to show this, and
> although the following is a
> simplification of my real code, it is closer to a concise but complete
> example...
>
>
> struct Settings{
> public int left, right, centre;
> }
>
> Settings set = new Settings();
> int ref intRef ; // ILLEGAL C# STATEMENT - note the use of "ref"
> if(???) intRef = set.left;
> else if(???) intRef = set.right;
> else intRef = set.centre;
>
> Then I would change the value that intRef points to.

I think the above is not a literal example of what you're trying to do.
After all, if the "int ref" were actually in the same method, it would
be simple enough to just set the field explicitly in the conditional:

if (???)
set.left = ...;
else if (???)
set.right = ...;
else
set.centre = ...;

So then the question is, what is the actual context here? Why is it
that you have a conditional in one method, that then needs to be acted
upon somewhere else? There _might_ be a better way to accomplish what
you're doing, but genuine specifics would be needed in order to answer
the question.

And for what it's worth, while I really like C#, the fact is that in
its simplicity (which I think is a good thing) it has left out some
kinds of things you could do in other languages (like C++). Now and
then, you may actually run across something that simply can't be done
in the same way, and occasionally that means you need to write more
explicit code.

(I hesitate to mention reflection, which is the "back door" sort of way
to deal with some situations that are like this one; it would be
possible to obtain something that's essentially like a reference to the
property or field you're trying to set by using reflection, but IMHO
reflection should be avoided unless there's really literally no other
way to implement the behavior you want, which doesn't appear to be the
case here).

Pete

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