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digitalmars.D.learn - Is "is" the same as ptr == ptr for arrays?

reply simendsjo <simen.endsjo pandavre.com> writes:
Is the following equalent?

int[] a;
int[] b = a;
assert(a is b);
assert(a.ptr == b.ptr);
Aug 07 2010
parent reply 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.
Aug 07 2010
next sibling parent 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);
Aug 07 2010
prev sibling parent reply "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
Aug 07 2010
parent 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><
Aug 07 2010