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6798 :: Reversed traversal of iterators instead of creating a reversed copy

• adokitkat (orginal) [2020-09-11T02:08:23+02:00] view original

  Hi,

  I think there should be a 'reverse' macro for reversed traversal of iterators which doesn't change the original content nor creates a duplicate (or something similar) - I tried to search for something like this but I did find only procs algorithm.reverse(), algorithm.reversed() which reverse the seq itself. Sorry if a such thing exists...

  Example:

  let arr = @[1,2,3,4]
  
  for item in arr.reversedTraversal(): # No copy created
    echo item
    # 4
    # 3
    # 2
    # 1
  
  # Maybe even this?
  echo arr.reversedTraversal() # @[4,3,2,1]
  
  # Original not changed
  echo arr # @[1,2,3,4]
  
  Run

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• TinBryn (orginal) [2020-09-11T05:04:49+02:00] view original

  I agree that it should be in the stdlib, but it's fairly easy to implement

  iterator reversed*[T](arr: openArray[T]): T =
    for it in countdown(arr.high, arr.low):
      yield arr[it]
  Run

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• enthus1ast (orginal) [2020-09-11T07:31:38+02:00] view original

  I think this Is not possible for all iterator. For arrays it's easy sure, but imagine eg a network stream. The last data may have not arrived already, or might never end etc..

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• Arrrrrrrrr (orginal) [2020-09-11T12:38:20+02:00] view original

  Yeah, an 'ritems/mritems' would be nice, I used the countdown iterator for that purpouse so many times it is strange why I haven't defined my own iterator at this point.

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• adokitkat (orginal) [2020-09-11T15:07:10+02:00] view original

  Thank you for a nice solution :) I went straight for a macro not considering overloading of an implicit iterator...

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