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454 :: Cannot prove that 'result' is initialized

• gradha (orginal) [2014-05-23T23:10:08+02:00] view original

  The following sample shows a typical construct in my programs, where I first define a init() proc and then a shortcut initFoo() to simplify var declarations:

  
  type
    Something = object
      name: string not nil
  
  proc init(X: var Something) =
    X.name = "Default"
  
  proc initSomething(): Something =
    result.init() # Cannot prove that 'result' is initialized
  
  proc test() =
    var s = initSomething()
    echo s.name
  
  when isMainModule: test()
  Run

  The line marked with the comment shows a compiler warning:

  
  prove.nim(9, 2) Warning: Cannot prove that 'result' is initialized. This will become a compile time error in the future. [ProveInit]
  Run

  I don't understand where the problem is. Can somebody explain why this pattern will become a compile time error in the future?

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• Araq (orginal) [2014-05-24T09:49:01+02:00] view original

  Because the compiler does not track what your init does, it cannot know that result.init sets the name field to a not-nil string. Surely we can make the compiler smarter instead of error'ing in the future. I wouldn't worry about it, others complained about it too so it's obvious the current way is not sufficient.

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