Comment #0 by bearophile_hugs — 2010-03-20T05:57:22Z
This D2 code is currrently allowed, but I think it has to become a syntax error, dynamic arrays are not pointers:
void main() {
int[] a1 = [5, 4, 3];
assert(*a1 == 5);
alias typeof(a1) T1;
assert(is(typeof(*T1)));
int* p1 = cast(int*)a1;
assert(p1 == a1.ptr);
}
----------------
Similar code can be written for a fixed-size array like:
int[3] a2 = [5, 4, 3];
For fixed-size arrays such conversions to pointers can be more acceptable.
Comment #1 by bearophile_hugs — 2010-05-06T04:15:13Z
Another case that I think is related:
import std.stdio: writeln;
struct Arr(int N) {
int[N] data;
alias data this;
}
void main() {
auto p = new Arr!(10);
*p = 10;
writeln(p.data); // Output: 10 10 10 10 10 10 10 10 10 10
}
Comment #2 by bearophile_hugs — 2011-04-26T10:39:52Z
(In reply to comment #0)
1.
> assert(*a1 == 5);
> alias typeof(a1) T1;
> assert(is(typeof(*T1)));
Dereferencing dynamic or static array without -d option is deprecated.
I think this is 'accepts-invalid'.
2.
> int* p1 = cast(int*)a1;
> assert(p1 == a1.ptr);
Explicit casting is still valid.
cast(int*)a1
means
cast(int*)a1.ptr
Comment #4 by k.hara.pg — 2011-10-31T04:33:36Z
(In reply to comment #1)
This is not related.
> auto p = new Arr!(10);
> *p = 10;
means
Arr!(10)* p = new Arr!(10);
(*p).data = 10; // see alias this after deref-ing of p
And, the assignment an element type into static array is valid.
int[10] sa;
sa = 10; // translated to sa[] = 10
Comment #5 by bearophile_hugs — 2011-10-31T05:36:43Z
(In reply to comment #3)
> > assert(*a1 == 5);
> > alias typeof(a1) T1;
> > assert(is(typeof(*T1)));
>
> Dereferencing dynamic or static array without -d option is deprecated.
> I think this is 'accepts-invalid'.
Don agrees:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=148054
> 2.
> > int* p1 = cast(int*)a1;
> > assert(p1 == a1.ptr);
>
> Explicit casting is still valid.
>
> cast(int*)a1
>
> means
>
> cast(int*)a1.ptr
I don't see the need to accept this cast. There is the ".ptr" so this cast is not useful in practice. And generally this cast is refused by DMD 2.056 as you see in the following program, so you are introducing/leaving an useless special case:
struct Foo {
int* p;
size_t n;
}
void main() {
Foo f;
auto x = cast(int*)f;
}
So I think cast(int*)a1 should be forbidden.
Comment #6 by bearophile_hugs — 2011-10-31T05:39:53Z
(In reply to comment #4)
> This is not related.
You are right, it's not related, it's a different problem.
> And, the assignment an element type into static array is valid.
>
> int[10] sa;
> sa = 10; // translated to sa[] = 10
It's currently valid, but I think it should be forbidden. I think D should require the [] here. See bug 3971
Comment #7 by k.hara.pg — 2011-10-31T07:43:01Z
(In reply to comment #5)
> I don't see the need to accept this cast. There is the ".ptr" so this cast is
> not useful in practice. And generally this cast is refused by DMD 2.056 as you
> see in the following program, so you are introducing/leaving an useless special
> case:
>
[snip]
> So I think cast(int*)a1 should be forbidden.
The title of this issue is "Deferencing a dynamic array as pointer".
Therefore even if you think it is not useful, we should not discuss it in here.
Instead, you can file it as a new issue.
Comment #9 by bearophile_hugs — 2011-10-31T12:24:36Z
(In reply to comment #7)
Thank you for the patch.
> The title of this issue is "Deferencing a dynamic array as pointer".
> Therefore even if you think it is not useful, we should not discuss it in here.
>
> Instead, you can file it as a new issue.
I have lumped them together because to me they look like quite similar issues: in both cases an array is seen as a pointer. But OK, I have opened the new report bug 6869