On Sunday, 11 May 2014 at 16:54:18 UTC, Ali Çehreli wrote:
On 05/11/2014 07:46 AM, rbutler wrote:
> I have searched and can not understand something about
passing AAs to a
> function.
> I have reduced the gist of the question to a tiny program
below.
> If I put "ref" in the function stmt it works, i.e.:
> ref int[int] aa
> My confusion is that AAs are supposed to be passed as refs
anyway, so I do
> not understand why I should have to use ref to make it work.
>
> Related, it also works if I UN-comment the line d[9] = 9;
>
> Thanks for any helpful comments you can make.
> --rbutler
>
> import std.stdio;
>
> void test(int[int] aa, int x) {
> aa[x] = x;
> aa[8] = 8;
> }
>
> void main() {
> int[int] d;
> writeln(d.length);
> // d[9] = 9;
> test(d, 0);
> writeln(d);
> }
The problem is with the initial state of associative arrays,
which happens to be null. When AAs are copied when null, both
copies are null, not being associated with anything, not even
an initial table to store the hash buckets in. As a result,
null AAs cannot be references to each other's (non existent)
data.
When a null AA starts receiving data, it first creates its own
data memory but the other one cannot know about that data.
ref parameter works because then there is only one AA to speak
of.
d[9] entry works as well because then the first AA is not null.
Ali
Remind me again why we can't just change this to a sensible
initial state? Or at least add a .initialize()?
