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6852 :: Same Regular Expression constructed in slightly different ways produces different results

• alexeypetrushin (orginal) [2020-09-23T14:14:58+02:00] view original

  This code would produce different results.

  I guess it's related to how string is escaped, it's confusing.

  import re
  
  echo "a b".split(re("\\s"))
  echo "a b".split(re"\\s")
  Run

  Result

  
  @["a", "b"]
  @["a b"]
  Run

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• cblake (orginal) [2020-09-23T14:31:21+02:00] view original

  The need for only one backslash in the second case { split(re"\\s") is the equivalent } is a feature not a bug. Anything can be confusing. :-/

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• DeletedUser (orginal) [2020-09-23T21:14:19+02:00] view original

  https://nim-lang.org/docs/manual.html#lexical-analysis-generalized-raw-string-literals

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• cblake (orginal) [2020-09-23T21:56:29+02:00] view original

  Python introduced raw string literals back in late 1997. Maybe some other prog.lang had them earlier? Even the C++11 standard picked them up. Nim's ideas along these lines are not unique (well, maybe more general..).

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• sschwarzer (orginal) [2020-09-24T00:18:38+02:00] view original

  In the first form the re is applied after the string literal is already parsed as a "normal" (non-raw) string \s. In the second form the string literal is parsed as a raw string \\s (see @Hlaaftana 's link).

  For what it's worth, I was wondering if there's a way to query the regex object for the string it was created from, but I didn't find anything in the re documentation. Trying to echo the regex gives a type error and printing the repr isn't helpful (for me at least ;-) ).

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• pietroppeter (orginal) [2020-09-24T00:36:37+02:00] view original

  I was wondering if there's a way to query the regex object for the string it was created from, but I didn't find anything in the re documentation.

  I do not think it is possible to recover original pattern in re, since Regex object only contains pointer to pcre objects: https://github.com/nim-lang/Nim/blob/version-1-2/lib/impure/re.nim#L46

  You can access directly the pattern if you use nre instead: https://nim-lang.org/docs/nre.html#Regex

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