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3133 :: Compile Time Evaluation of Constants From C-Header Files

• ivanitto (orginal) [2017-08-28T23:29:09+02:00] view original

  Is there a way to make nim compiler to evaluate constants from C-header files at compile time?

  For example, symbols S_IFREG and S_IFDIR (from posix.nim <- sys/stat.h) used in following code snippet:

  case x:
  of S_IFREG:  echo "file"
  of S_IFDIR:  echo "dir"
  else:        echo "other"
  Run

  are resulting in error "cannot evaluate at compile time: S_IFREG" because these symbols declared as 'var' in posix.nim, when they are constants actually. What would be a nice workaround for this?

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• jlp765 (orginal) [2017-08-29T00:08:19+02:00] view original

  Have a look at static

  
  static:
    # compile time stuff here
  Run

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• ivanitto (orginal) [2017-08-29T22:11:43+02:00] view original

  Thank you @jlp765, I know about the static, but asking about a different thing:

  Is there a way in nim language to use values of S_IFREG and S_IFDIR in the 'of' clause of the 'case-of' statement? (for example, like in the post above)

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• Araq (orginal) [2017-08-29T22:23:56+02:00] view original

  There is no solution but to patch posix.nim so that it knows the actual values for the popular OSes out there.

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• ivanitto (orginal) [2017-08-29T23:02:10+02:00] view original

  Thanks Andreas. Would you consider such a minor change in stdlib as desirable?

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• Araq (orginal) [2017-08-29T23:17:59+02:00] view original

  Minor change? Nim supports ~8 Posix-like OSes on ~5 different CPU architectures. I wrote a tool "detect.nim" to extract these values at build time (similar to what autoconf does) but it's not clear how to incorporate it into Nim's build system.

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