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9815 :: strutils: mapIt: empty seq gives index error

• freeflow (orginal) [2023-01-10T12:45:29+01:00] view original

  I'm seeing this error when I pass an empty seq to mapIt

  
  C:\Users\slayc\.choosenim\toolchains\nim-#devel\lib\system\fatal.nim(54) sysFatal
  Error: unhandled exception: index out of bounds, the container is empty [IndexDefect]
  Error: execution of an external program failed: 'c:\Users\slayc\source\repos\AdventOfCode\Nim\nim2022\src\MainModule.exe'
  Run

  Of course I can avoid this error by testing for len = 0 but I was wondering if I should raise this as an issue as mapIt should probably handle an empty sequence a bit more gracefully.

  Looking at the code for mapIt it doesn't seem that there is an explicit test for an empty seq.

  I am not a novice at nim programming. Such a claim would be implying I have far more competence and capability than in reality.

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• jrfondren (orginal) [2023-01-10T13:10:34+01:00] view original

  Passing an empty seq to mapIt works with devel and 1.6.10:

  import std/sequtils
  
  let
    nums: seq[int] = @[]
    strings = nums.mapIt($it)
  echo strings
  Run

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• freeflow (orginal) [2023-01-10T15:46:32+01:00] view original

  Thanks for the feedback.

  my comment came from this

  
  if myNewTracks.len > 0:
              var myTrackMin: int = myNewTracks.mapIt(it.len).min  - 1
              if myTrackMin < myMin:
                  myMin = myTrackMin
  Run

  where myNewTracks is a seq[seq[Coord]] and Coord is an object of col:int, row:int

  The test for zero was added because I was getting the error message at the mapIt line.

  my assumption is that the mapIt gives me a sequence of int (the lengths of the inner seq) and I then find the minimum value from that new seq.

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• freeflow (orginal) [2023-01-10T16:02:01+01:00] view original

  Yes, its an issue with min. My apologies for time wasting. I just refer you to the last line of my op.

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