https://issues.dlang.org/show_bug.cgi?id=12842

          Issue ID: 12842
           Summary: More support for ranges of ranges
           Product: D
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: Phobos
          Assignee: nobody@puremagic.com
          Reporter: john.loughran.colvin@gmail.com

std.range and std.algorithm often have support for an arbitrary number of ranges passed as seperate parameters, but very few offer range-of-range support.

Usage example:

auto a = [1,2,3,4];
auto b = [5,6,7,8,9];

//a rectangular matrix in flat form
auto cp = cartesianProduct(a, b).map!"a[0] * b[0]"();

//expand to RoR, take the transform and return to flat
auto cpT = cp.chunks(a.length).roundRobin().joiner();


Currently that doesn't work as roundRobin doesn't know how to handle ranges of ranges.

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