Faster sort?

[Andrea Fontana via Digitalmars-d]

On Thursday, 7 April 2016 at 08:41:51 UTC, John Colvin wrote:
> *hench my example of compiling one module to an object file and 
> then compiling the other and linking them, without ever 
> importing one from the other.

If i move boolSort() on another module but I can't use auto as 
return type.
Return type is a "voldemort" type returned by std.range.chain.

How can I define it?