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4654 :: Mix of varags & seq confusion

• teras (orginal) [2019-02-12T23:25:35+01:00] view original

  Hello people, new user of nim here and I am already excited! I have the following scenario, for test purposes, and I think I'm missing something here, or, in other words, how to make the compiler get what I mean?

  proc test(names:varargs[seq[string]]) = discard
  proc test(names:varargs[string]) = discard
  
  test "hello", "world"  # works
  test @["hello"], @["world"]  # works
  test @["hello", "world"]  # compiler error, I get an "ambiguous call"
  Run

  In my eyes this is not an "ambiguous call", since this is clearly a seq and not a varags. And this is obvious for me, since the two types are not interchangeable. So what I am missing here?

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• gemath (orginal) [2019-02-13T10:11:51+01:00] view original

  In this example

  proc test(names:varargs[string]) =
    for n in names:
      echo n
    echo "----"
  
  test "hello", "world"
  test @["hello", "world"]
  Run

  both calls work. The first call passes string arguments, they are implicitly converted to an openArray for the varargs proc as usual. Looking at the second call, the compiler thinks that you already did that conversion because it gets a seq, which is an openArray. So for the last call in your example, the compiler cannot decide whether you are trying to call the first proc with one argument or the second proc with two arguments.

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• teras (orginal) [2019-02-13T17:20:07+01:00] view original

  So, for me to understand.

  • The reason the last call does not work, is because there's a implicit matched conversion from seq => openArray => varags ?
  • I couldn't find a clear documentation, which types are converted to which, especially for these data types. Is there one anywhere?
  • Is there any way to hint the compiler which of these two versions of the syntax I want to use?

  Thanks!

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• mratsim (orginal) [2019-02-13T19:32:18+01:00] view original

  openarray matches with seq and arrays varargs matches with seq, arrays and variadic arguments like foo(1, 2, 3)

  You can only hint the compiler if they are in different files like fileA and fileB, you can use fileA.test and fileB.test

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• Arrrrrrrrr (orginal) [2019-02-14T09:53:48+01:00] view original

  Varargs

  A varargs parameter is an openarray parameter that additionally allows to pass a variable number of arguments to a procedure. The compiler converts the list of arguments to an array implicitly

  Open arrays

  Openarrays are always indexed with an int starting at position 0. The len, low and high operations are available for open arrays too.

  I think this documentation should clearly state that strings, seqs and arrays are openarrays (actually the only ones).

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• mratsim (orginal) [2019-02-14T10:57:37+01:00] view original

  Nitpick: strings are not openarray[char].

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• Arrrrrrrrr (orginal) [2019-02-14T11:27:02+01:00] view original

  But this works https://wandbox.org/permlink/y9EYLm0EV6ULzrqS. It is a conversion I'm not aware of?

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• serano33 (orginal) [2019-02-19T20:54:08+01:00] view original

  i cant fix that

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• mratsim (orginal) [2019-02-20T00:29:46+01:00] view original

  AFAIK this shouldn't work. I remember having to do proc fooT: not char in Arraymancer before https://github.com/nim-lang/Nim/issues/6350 was fixed, anyway not hijacking this thread anymore :P.

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