Struct verses class.

[archana]

Hi all,

Can someone tell me meaning of this stmt:-

'A structure must have at least one nonshared variable or event member;
a class can be completely empty'.

Because if i have code like
class a
{

}
struct a1
{
}

As above declaration i have declared class as well as struct with no
paramter. Still it is acceptable.

So can some one tell me what am i doing wrong and please clear me
reagrding above menion statement.

thanks in advance.

[Jon Skeet [C# MVP]]

archana wrote:

Can someone tell me meaning of this stmt:-

'A structure must have at least one nonshared variable or event member;
a class can be completely empty'.
That's completely incorrect.

<snip>
So can some one tell me what am i doing wrong and please clear me
reagrding above menion statement.

You're doing nothing wrong. Where did you hear the above statement? I'd
start treating any other statements from the same source with a pinch
of salt. (Of course, it's possible that that is the only incorrect
statement they've made - but it's worth checking.)

Jon

[Larry Lard]

Jon Skeet [C# MVP] wrote:

archana wrote:

Can someone tell me meaning of this stmt:-

'A structure must have at least one nonshared variable or event member;
a class can be completely empty'.
That's completely incorrect.

But true of the almost-equivalent things in VB.NET.
<snip>

So can some one tell me what am i doing wrong and please clear me
reagrding above menion statement.
You're doing nothing wrong. Where did you hear the above statement?

<http://msdn.microsoft. com/library/en-us/vbcn7/html/vaconStructures AndClasses.asp> ,
or similar, possibly.
I'd
start treating any other statements from the same source with a pinch
of salt. (Of course, it's possible that that is the only incorrect
statement they've made - but it's worth checking.)

Context is everything, isn't it :)

--
Larry Lard
Replies to group please

[archana]

Hi Jon,

Thanks for your reply.

Larry has providied link of document which contains this statement.

Thats why i was asking question.

thanks

Jon Skeet [C# MVP] wrote:

archana wrote:

Can someone tell me meaning of this stmt:-

'A structure must have at least one nonshared variable or event member;
a class can be completely empty'.

That's completely incorrect.

<snip>

So can some one tell me what am i doing wrong and please clear me
reagrding above menion statement.

You're doing nothing wrong. Where did you hear the above statement? I'd
start treating any other statements from the same source with a pinch
of salt. (Of course, it's possible that that is the only incorrect
statement they've made - but it's worth checking.)

Jon

[Jon Skeet [C# MVP]]

archana <tr************ **@yahoo.com> wrote:

Thanks for your reply.

Larry has providied link of document which contains this statement.

Thats why i was asking question.

Right. I've no idea why VB.NET has that restriction, but C# certainly
doesn't.

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

[Mattias Sjögren]

>Right. I've no idea why VB.NET has that restriction, but C# certainly

doesn't.

Not much of a restriction in practice, is it? What good is an empty
struct anyway? If you only have static members you may as well us a
static class.

The CLR requires value types to either have instance fields or an
explicit size so for empty structs the C# compiler must effectively
add [StructLayout(.. ., Size=1)]. So now you have a type that appears
to be empty but still actually takes up one byte. I'm not sure I like
that better than what the VB compiler is doing.
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Göran Andersson]

Mattias Sjögren wrote:

Right. I've no idea why VB.NET has that restriction, but C# certainly
doesn't.

Not much of a restriction in practice, is it? What good is an empty
struct anyway? If you only have static members you may as well us a
static class.

The CLR requires value types to either have instance fields or an
explicit size so for empty structs the C# compiler must effectively
add [StructLayout(.. ., Size=1)]. So now you have a type that appears
to be empty but still actually takes up one byte. I'm not sure I like
that better than what the VB compiler is doing.
Mattias

Truly not a restriction in practice.

I can not come up with a single use for an empty structure. A value type
that doesn't carry it's own value is totally useless.

The closest thing to something useful I can think of is creating
different empty structures that would override the ToString method and
return different values. Then you could put instances of the different
structs in something like an ArrayList, and then you could use the
ToString method on the objects in the ArrayList without needing to know
what structure it really was, and they would return different values.
But then again you could just put the strings in the ArrayList and it
would have exactly the same effect...

[Mark Wilden]

"Göran Andersson" <gu***@guffa.co m> wrote in message
news:O4******** ******@TK2MSFTN GP03.phx.gbl...

I can not come up with a single use for an empty structure. A value type
that doesn't carry it's own value is totally useless.

Yes. An empty class can be useful, as a placeholder for derived behavior you
know you'll eventually add, but that doesn't apply to structs.

///ark