compile time 'address'

[Dominic Jones]

On Thursday, 29 November 2018 at 18:49:27 UTC, Steven 
Schveighoffer wrote:

> Ah, ok. Essentially you are looking for the layout of the local 
> variables.
>
> One thing that is available for D is the compile-time property 
> offsetof, which gives the offset from the start of an aggregate 
> that an item is.
>
> for example:
>
> struct S
> {
>   int x;
>   bool y;
> }
>
> static assert(S.y.offsetof == 4);
>
> So while this isn't available for function locals, the idea is 
> similar. But I don't think there's an equivalent to what you 
> are able to do here in C++.
>
> I don't think it would be a huge stretch to apply this same 
> property to function locals, but it would require an 
> enhancement request.


This is an interesting idea.

Somehow it would be helpful to access the frame pointer, too, 
from the variable. Obtaining this offset via the variable would 
enable disambiguation between variables with the same local 
offset but from different functions.


The example would then read something like:

auto cmp(T, U)(const ref T t, const ref U u)
{
   // i.e.
   //   t.frame.offsetof := &main;
   //   t.offsetof := main.c0.offsetof;

   enum f = t.frame.offsetof == u.frame.offsetof;
   enum v = t.offsetof == u.offsetof;
   return f && v;
}

void main()
{
   auto c0 = 1;
   auto c1 = 2;

   static assert(cmp(c0, c0));
   static assert(!cmp(c0, c1));
}