http://d.puremagic.com/issues/show_bug.cgi?id=9507

           Summary: std.range.transposed behaves poorly with jagged ranges
                    of ranges
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: hsteoh@quickfur.ath.cx


--- Comment #0 from hsteoh@quickfur.ath.cx 2013-02-13 13:32:56 PST ---
If you pass a jagged range of ranges to std.range.transposed, once one of the subranges is consumed, .front will cause an invalid access to the empty subrange's .front, causing a runtime error.

However, the returned range's .empty will still be false, even though you can't safely use .front anymore!

So std.range.transposed should either return empty if *any* of its ranges are empty, or else, its .front should be modified so that empty subranges will be skipped over (or should there be an option to specify a default element?).

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http://d.puremagic.com/issues/show_bug.cgi?id=9507


bearophile_hugs@eml.cc changed:

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--- Comment #1 from bearophile_hugs@eml.cc 2013-03-03 17:35:46 PST ---
(In reply to comment #0)
> If you pass a jagged range of ranges to std.range.transposed, once one of the subranges is consumed, .front will cause an invalid access to the empty subrange's .front, causing a runtime error.
> 
> However, the returned range's .empty will still be false, even though you can't safely use .front anymore!
> 
> So std.range.transposed should either return empty if *any* of its ranges are empty, or else, its .front should be modified so that empty subranges will be skipped over (or should there be an option to specify a default element?).

This shows some usages the stadard Haskell function transpose, I'd like the D version to do something similar. No need for a default element:

Prelude> import Data.List (transpose)
Prelude Data.List> transpose [[1,2,3],[4,5,6],[7,8,9]]
[[1,4,7],[2,5,8],[3,6,9]]
Prelude Data.List> let a =
[[7,4,2,8,7],[8,0,8],[3],[1,6,0,7,7,2,0],[8,9,3,1],[6],[6]]
Prelude Data.List> transpose a
[[7,8,3,1,8,6,6],[4,0,6,9],[2,8,0,3],[8,7,1],[7,7],[2],[0]]
Prelude Data.List> transpose [[1],[],[3,4]]
[[1,3],[4]]

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