We need to have a way to say "convert this nested function into a struct"

[Idan Arye via Digitalmars-d]

On Saturday, 6 June 2015 at 06:16:17 UTC, Andrei Alexandrescu 
wrote:
> Nested functions that allocate their environment dynamically 
> can be quite useful. However, oftentimes the need is to convert 
> the code plus the data needed into an anonymous struct that 
> copies the state inside, similar to C++ lambdas that capture by 
> value.
>
> I wonder how to integrate that within the language nicely.
>
>
> Andrei

My solution: http://dpaste.dzfl.pl/aa013ff51f60

Can't make it @nogc though, because it thinks I'm trying to 
capture `a` and `b`...