More general Cartesian product

[Magnus Lie Hetland]

Hi!

I have a need for a Cartesian product of multiple ranges. I see there's 
been a discussion here (Dec 2011) as well as a request posted (#7128). 
It seems to me that the request deals with a multidimensional product 
-- which is what I need -- while the implementation by Timon Gehr deals 
only with the two-dimensional case.

I guess I could apply it in a nested fashion, but there's still the 
issue of flattening the result.

My application is a template along the lines of

  void forall(alias func, T...)(T args) {
    ...
  }

which would call func with every combination of parameters taken from 
the ranges in args. So that, for example, forall!foo([1, 2], ["a", 
"b"]) would yield four calls, from foo(1, "a") to foo(2, "b").

But the thing is that I'd like an arbitrary number of arguments. Sure, 
I could set an upper limit and hard-code the cases -- but there must be 
a prettier way? I've made some stabs at a recursive version, DMD 
complaining all the while. Any pointers?

(Now, I would eventually like to do more complex versions, using only a 
*subset* of the Cartesian product (for, e.g., all-pairs testing or 
combinatorial testing).)

-- 
Magnus Lie Hetland
http://hetland.org