newCTFE: perliminary delegate support is in!

[Cym13]

On Wednesday, 13 June 2018 at 05:57:31 UTC, Stefan Koch wrote:
> Good day ladies and gentleman,
>
> it is my distinct please to announce that a new feature just 
> landed in newCTFE.
>
> !!! DELEGATES !!!
>
> this means the following code will now work:
> int square_of_x_plus_x(int x) pure
> {
>     int passThrough(int y) pure
>     {
>         assert(x == y);
>         int y2 = x;
>         assert(y2 == y);
>
>         int fnC() pure
>         {
>             auto z = (x * y);
>             assert(y2 == x);
>             assert(x == y);
>             return z;
>         }
>         return fnC();
>     }
>     return x + passThrough(x);
> }
>
> pragma(msg, square_of_x_plus_x(7));
> static assert(square_of_x_plus_x(5) == (5*5)+5);
>
> the reason why this was quite tricky to implement is that
> in the newCTFE architecture there is no concept of a function 
> touching
> the stack-frame of another function _at all_.
> (Infact there is  no conventional stack, rather the virtual 
> registers themselves stack)
> Sharing of the stack frames gets emulated via a hidden 
> parameter and a linked-list structure.
>
> Cheers,
> Stefan

That's very nice! Out of curiosity, what was the reason to avoid 
a conventional stack? Or was it a consequence more than a design 
decision? (If you've explained it before, feel free to just throw 
the old post at me)