How to create friends of a class at compile time?

[Tejas]

>
> If, however, you're trying to inject friend access to something 
> outside def's module, then you might want to reconsider what 
> you're trying to accomplish and whether it can be done 
> differently.
>
>
> 

Was just dreaming of how to transpile C++ code to D :(
Curiously enough,  friend injection was not made part of the 
standard back in 1998 and only g++ supported it through a 
non-standard extension. But now here we are. I wonder why this 
was allowed.