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2556 :: General Performance tips?

• perturbation2 (orginal) [2016-09-28T09:29:32+02:00] view original

  Are there any general performance tips that you've come across that aren't immediately obvious?

  Stuff like:

  • Sequence / String assignment uses copying semantics (and avoiding with {.shallow.} or ref)
  • Avoiding hidden allocations
  • Good patterns for submitting easily parallelizable stuff to the threadpool
  • Effectively using slices to avoid allocations
  • Append vs add vs '&' for sequences and strings

  If performance is an issue I usually just try to profile with Apple's profiling tools in XCode or the equivalent in Linux, but I don't feel like I've developed a sense yet for how to write really idiomatic, performant code "the first time".

  If nothing else, it would be a good blog post ;)

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• jlp765 (orginal) [2016-09-29T03:59:43+02:00] view original

  compile with -d:release :-)

  avoid seq add() in loops if you can do a setLen before the loop then reference seq items

  use let rather than var in loops when possible and appropriate

  avoid string modifications or allocations if possible

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• euant (orginal) [2016-09-29T10:43:46+02:00] view original

  Use a main() proc combined with when isMainModule: rather than putting main code in the top level.

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• OderWat (orginal) [2016-09-29T12:22:35+02:00] view original

  Why would I need when isMainModule: for code which would be global otherwise?

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• euant (orginal) [2016-09-29T13:18:06+02:00] view original

  @OderWat: True, I personally use it for sanity as it makes it easy to search within projects for things that may be ran globally.

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• def (orginal) [2016-09-29T13:33:59+02:00] view original

  @OderWat: For example http://forum.nim-lang.org/t/503

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• OderWat (orginal) [2016-09-29T13:46:24+02:00] view original

  @def I mean to ask why there would be a difference between:

  proc main() = discard
  when isMainModule:
    main()
  Run

  instead of just:

  proc main() = discard
  main()
  Run

  @euant I can't follow that reasoning. I use "when isMainModule" for test code in libraries or to try quickly stuff in modules which normally get included but are in development. It would not mean anything regading "global code" if I scanned my codebase for "isMainModule". It would if I scan for main() though, as this is what I use instead of "global" usually now.

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• euant (orginal) [2016-09-29T15:46:30+02:00] view original

  @OderWat: I rarely ever write my test code inside modules, I use the unittest module for that :) It all comes down to personal preference really, and my background and past experience makes me favour splitting my test code into other areas.

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• OderWat (orginal) [2016-09-29T16:40:59+02:00] view original

  @euant I still think your usage of when isMainModule: is unusual and imho neither good practice nor an optimisation. I believe in using when isMainModule: to compile code only when it is compiled as main module :)

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• euant (orginal) [2016-09-29T17:22:40+02:00] view original

  @OderWat: I definitely see where you're coming from, but it would be hard for me to drop my bad habits now ;)

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