DIP 1018--The Copy Constructor--Community Review Round 1

[12345swordy]

On Wednesday, 19 December 2018 at 11:53:12 UTC, Kagamin wrote:
> I think const postblit can be done by creating shadow copy of 
> instance fields (but still physically located in the field).
>
> struct A
> {
>     int b;
>     this(this) immutable
>     {
>         immutable int shadow_b; //reads go here
>         //b++
>         immutable int t=shadow_b;
>         shadow_b.__dtor();
>         b.__ctor(t+1);
>     }
> }
>
> Type system would treat them as distinct instances, but would 
> destroy shadow copy right before assignment, after which shadow 
> copy's lifetime ends and it goes out of scope completely, which 
> will also invalidate any retained pointers if any.

You should not be resorting to calling the hidden symbol .__dtor, 
.__ctor in your production code as that is just asking for 
trouble. Which it is not guarantee to grant the behavior that you 
desire.

Alex