More range woes: composed ranges are unsafe to return from functions

[jerro]

On Tuesday, 16 October 2012 at 19:31:18 UTC, H. S. Teoh wrote:
> On Tue, Oct 16, 2012 at 08:44:56PM +0200, monarch_dodra wrote:
> [...]
>> No idea either, but I'll volunteer to investigate ;)
>> 
>> I agree with Jonathan though, sounds like a bug somewhere. 
>> There
>> is no reason for your code to fail.
>> 
>> I'll post back if I find anything.
>
> Another data point: if I move the .joiner call out of cprod() 
> into
> main(), then there is no problem. Could it be that something in 
> joiner
> is breaking somehow, when returned from a function?
>
>
> T

I don't know, but if I change the code to this:

auto cprod(R1,R2)(R1 A, R2 B) {
     // This part is exactly the same as in main(), below. So
     // in theory, it should work exactly the same way.
     auto mapper = (typeof(tuple(cast(size_t) 0, A.front, 
B.front)) a) => chain(
                     zip(repeat(a[1]), B.save.take(a[0])),
                     zip(A.save.take(a[0]+1), repeat(a[2])));

     auto r = zip(sequence!"n"(cast(size_t)0), A.save, B.save)
         .map!mapper()
         .joiner;

     // But something goes wrong here: is it because the
     // above composed ranges are stack-allocated temporaries
     // that go out of scope upon return?
     return r;
}

It works too.