• simendsjo <simen.endsjo pandavre.com> Aug 07 2010
• Peter Alexander <peter.alexander.au gmail.com> Aug 07 2010
• simendsjo <simen.endsjo pandavre.com> Aug 07 2010
• "Simen kjaeraas" <simen.kjaras gmail.com> Aug 07 2010
• BCS <none anon.com> Aug 07 2010

simendsjo <simen.endsjo pandavre.com> writes:

Is the following equalent?

int[] a;
int[] b = a;
assert(a is b);
assert(a.ptr == b.ptr);

Peter Alexander <peter.alexander.au gmail.com> writes:

On 7/08/10 4:33 PM, simendsjo wrote:
 Is the following equalent?

 int[] a;
 int[] b = a;
 assert(a is b);
 assert(a.ptr == b.ptr);


No.

(a is b) implies (a.ptr == b.ptr)

but

(a.ptr == b.ptr) does not imply (a is b)

For example:

int[] a = [1, 2, 3];
int[] b = a[0..1];

Here, a.ptr == b.ptr, but a !is b.

The ptr property returns a pointer to the first element, which is true 
in this case, but it doesn't mean that they both refer to the same range.

simendsjo <simen.endsjo pandavre.com> writes:

On 07.08.2010 18:04, Peter Alexander wrote:
 On 7/08/10 4:33 PM, simendsjo wrote:
 Is the following equalent?

 int[] a;
 int[] b = a;
 assert(a is b);
 assert(a.ptr == b.ptr);


 No.

 (a is b) implies (a.ptr == b.ptr)

 but

 (a.ptr == b.ptr) does not imply (a is b)

 For example:

 int[] a = [1, 2, 3];
 int[] b = a[0..1];

 Here, a.ptr == b.ptr, but a !is b.

 The ptr property returns a pointer to the first element, which is true
 in this case, but it doesn't mean that they both refer to the same range.



Ok, thanks. Does this mean this equivalent then?

int[] a = [1,2,3];
int[] b = a[0..1];
assert(a !is b);
assert(a.ptr == b.ptr && a.length == b.length);

"Simen kjaeraas" <simen.kjaras gmail.com> writes:

simendsjo <simen.endsjo pandavre.com> wrote:

 Ok, thanks. Does this mean this equivalent then?

 int[] a = [1,2,3];
 int[] b = a[0..1];
 assert(a !is b);
 assert(a.ptr == b.ptr && a.length == b.length);


Well, no. But what you probably mean, is.

( a is b ) == ( a.ptr == b.ptr && a.length == b.length )

-- 
Simen

BCS <none anon.com> writes:

Hello Simen,

 simendsjo <simen.endsjo pandavre.com> wrote:
 
 Ok, thanks. Does this mean this equivalent then?
 
 int[] a = [1,2,3];
 int[] b = a[0..1];
 assert(a !is b);
 assert(a.ptr == b.ptr && a.length == b.length);




both asserts will fail (a.length == 3 != b.length == 1)

 But what you probably mean, is.
 
 ( a is b ) == ( a.ptr == b.ptr && a.length == b.length )


I think that is correct.

-- 
... <IXOYE><