Disallow arrays as pointers

bearophile bearophileHUGS at lycos.com
Mon Oct 31 12:34:59 PDT 2011


Kenji Hara (and the D community) is really good, he has already written a pull request with the bug fix:
https://github.com/D-Programming-Language/dmd/pull/483

---------------------

Kenji Hara has fixed about 1/3 of the issue, so he asked me to split the but report, this is a spin off:
http://d.puremagic.com/issues/show_bug.cgi?id=6869

In DMD 2.056 this code compiles:

void main() {
   int[] a1 = [5, 4, 3];
   int* p1 = cast(int*)a1; // no compile error here
}


Similar code using user-created struct doesn't compile:


struct Foo {
    int* p;
    size_t n;
}
void main() {
    Foo f;
    auto x = cast(int*)f; // compile error here
}


I don't see the need to accept this cast, because we have said that D arrays are not pointers, and allowing the array to pointer cast means introducing/leaving an useless special case, and in practice this special case is not useful because arrays have the ptr property:


struct Foo {
    int* p;
    size_t n;
}
void main() {
    Foo f;
    auto x = f.ptr; // OK
}


So I think cast(int*)a1 should be forbidden.

-----------------------

The third part of the bug report was part of this older one:
http://d.puremagic.com/issues/show_bug.cgi?id=3971

The idea is to forbid code like:

void main() {
   int[3] a;
   a = 1;
   assert(a == [1, 1, 1]);
}


And require the square brackets every time an array operation is performed, for syntactic uniformity with the other vector ops, and to avoid mistakes:


void main() {
   int[3] a;
   a[] = 1;
   assert(a == [1, 1, 1]);
}

Bye,
bearophile


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