Is the following equalent?

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

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.

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);

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

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);
> Well, no. 

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><