Is "auto t=T();" not the same as "T t;"?

[Paul Backus]

On Tuesday, 25 October 2022 at 16:52:48 UTC, Salih Dincer wrote:
> On Tuesday, 25 October 2022 at 13:51:30 UTC, Andrey Zherikov 
> wrote:
>> Does the second piece of code shows a bug or my expectation is 
>> not correct (and why if so)?
>
> This is a bug:
>
> ```d
> void main()
> {
>   struct B
>   {
>     struct A
>     {
>       int i = 10;
>     }
>     A[] a = [A.init];
>   }
>
>   B[2] b;
>   assert(b[0].a[0].i == 10);
>   assert(b[1].a[0].i == 10);
>
>   b[0].a[0].i = 1;
>   assert(b[0].a[0].i == 1); // ok...
>   assert(b[1].a[0].i == 1); // must be 10 !!!
> }
> ```

It's not a bug. They're pointing to the exact same instance of 
`A` in memory:

```d
void main()
{
   struct B
   {
     struct A
     {
       int i = 10;
     }
     A[] a = [A.init];
   }

   B[2] b;
   assert(b[0].a.ptr is b[1].a.ptr);
}
```

As explained in [Adam's reply][1], what happens here is that 
there is a single, global `A[]` allocated at compile time, which 
is shared between all instances of `B.init`. It's the same as if 
you'd written

```d
struct B
{
     struct A
     {
         int i = 10;
     }
     static A[] globalArray = [A.init];
     A[] a = globalArray;
}
```

[1]: 
https://forum.dlang.org/post/yznhocajstphrozpnqzo@forum.dlang.org