Optional parameters referring to previous parameters?

[Tove]

On Thursday, 10 May 2012 at 15:51:08 UTC, Steven Schveighoffer 
wrote:
> On Thu, 10 May 2012 11:48:25 -0400, Steven Schveighoffer 
> <schveiguy at yahoo.com> wrote:
>
> And BTW, it's not just sugar -- you are saving a function call 
> and unnecessary code space.
>
> -Steve

ui, pretty please! I love it too, it would allow this marvelous 
construct!

auto my_extended_alloca(size_t size, void* buf=alloca(size))
{
   return buf;
}