about struct (e.g. System.Drawing.Point)

[Action]

Point is a struct
but I can do both

Point a;
Write(a.X);
Write(a.Y);

and
Point a = new Point(1,1);
Write(a.X);
Write(a.Y);
.....seems confusing!

[Jon Skeet]

Re: about struct (e.g. System.Drawing. Point)

Action <amuro@hotmail. com> wrote:[color=blue]
> Point is a struct
> but I can do both
>
> Point a;
> Write(a.X);
> Write(a.Y);[/color]

Yes, although it's a bad idea to do that - I'd always write the above
as

Point a = new Point();
Write (a.X);
Write (a.Y);

It'll do the same thing (always, I believe) but it means that the whole
of the struct is definitely assigned.
[color=blue]
> and
> Point a = new Point(1,1);
> Write(a.X);
> Write(a.Y);
> ....seems confusing![/color]

Why? Basically "new" returns a new *value* for value-types, not a new
reference.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Action]

Re: about struct (e.g. System.Drawing. Point)

Does this mean that
Point a = new Point(1,2);
Write (a.X);
Write (a.Y);
1. a new Point is created
2. Value of the newly created Point is assigned to Point "a"
3. the "new Point" is destroyed, as Point "a" is a struct, it didn't really
points to the "new Point", so the "new Point" has zero reference => GC clean
it up....

is this the case?
thx!

"Jon Skeet" <skeet@pobox.co m> wrote in message
news:MPG.19db68 d27e7b99b989741 @news.microsoft .com...[color=blue]
> Action <amuro@hotmail. com> wrote:[color=green]
> > Point is a struct
> > but I can do both
> >
> > Point a;
> > Write(a.X);
> > Write(a.Y);[/color]
>
> Yes, although it's a bad idea to do that - I'd always write the above
> as
>
> Point a = new Point();
> Write (a.X);
> Write (a.Y);
>
> It'll do the same thing (always, I believe) but it means that the whole
> of the struct is definitely assigned.
>[color=green]
> > and
> > Point a = new Point(1,1);
> > Write(a.X);
> > Write(a.Y);
> > ....seems confusing![/color]
>
> Why? Basically "new" returns a new *value* for value-types, not a new
> reference.
>
> --
> Jon Skeet - <skeet@pobox.co m>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too[/color]

[Jon Skeet]

Re: about struct (e.g. System.Drawing. Point)

Action <amuro@hotmail. com> wrote:[color=blue]
> Does this mean that
> Point a = new Point(1,2);
> Write (a.X);
> Write (a.Y);
> 1. a new Point is created
> 2. Value of the newly created Point is assigned to Point "a"
> 3. the "new Point" is destroyed, as Point "a" is a struct, it didn't really
> points to the "new Point", so the "new Point" has zero reference => GC clean
> it up....
>
> is this the case?[/color]

Not quite - because Point is a value type, there *is* nothing on the
heap to be cleaned up. It's just the same as doing:

int a=5;
int b=10;
int x = a+b;

- the addition is performed, and the value is assigned to x. Exactly
the same kind of thing is happening here - the point is created, and
then assigned to the variable. At no point does anything need to be on
the heap - there are no references involved.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too