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3026 :: "Warning: Cannot prove that 'result' is initialized"

• rxi (orginal) [2017-07-01T17:16:12+02:00] view original

  Unsure what I should be doing differently in the following code as to prevent the warnings:

  import strutils
  
  type MouseButton* = enum
    mbLeft = 1
    mbMiddle = 2
    mbRight = 3
  
  let s = "mbLeft"
  let m = parseEnum[MouseButton](s)
  echo m
  Run

  Warnings:

  
  test.nim(9, 18) template/generic instantiation from here
  lib/pure/strutils.nim(994, 3) Warning: Cannot prove that 'result' is initialized. This will become a compile time error in the future. [ProveInit]
  test.nim(9, 5) Warning: Cannot prove that 'm' is initialized. This will become a compile time error in the future. [ProveInit]
  Run

  Any suggestions would be appreciated, thanks!

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• leledumbo (orginal) [2017-07-02T09:09:56+02:00] view original

  The warning comes from parseEnum implementation, just propagated to your code (if the return value cannot be proven to have been initialized, then so does the variable holding it). Simply ignore for now, when the compiler changes this behavior to compile time error, the implementation should have also been fixed. From parseEnum code, return value is always initialized or an exception shall be raised (probably the compiler cannot yet incorporate exception into the proving algorithm).

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• stisa (orginal) [2017-07-02T15:33:37+02:00] view original

  You can avoid the warning by having the enum start at 0:

  type MouseButton* = enum
    mbNone
    mbLeft = 1
    mbMiddle = 2
    mbRight = 3
  Run

  Since enum default to the value 0, and your enum starts at 1, the default value of your enum is invalid:

  type MouseButton* = enum
    mbLeft = 1
    mbMiddle = 2
  
  var ml : MouseButton
  echo ml #> 0 (invalid data!)
  Run

  Actually, I think that you can make it start from whatever value you want, eg. -23, as long as your enum contains a value for 0, but I haven't tested it.

  (note that even if you start from a negative number, the default value of the enum is the one that corresponds to 0, not the first one in the list)

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• rxi (orginal) [2017-07-03T20:09:48+02:00] view original

  Thanks for the solution and explanation, stisa! The change you suggested solved the problem.

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